Fiqh linguistically means understanding. Technically in religion, it has two meanings: 

1. Knowing and understanding the rulings that pertain to the actions of the people. For example, knowing when and under what circumstances something becomes forbidden, permissible, required, etc. 
2. The rulings themselves. For example, knowing that such and such thing is forbidden, permissible, required, etc.

Simply put, Fiqh is concerned with the extraction of Islamic rulings through Islamic sources (Quran, hadith, etc.), which are studied under Usul-ul-Fiqh. In other words, Fiqh is the end result while Usul-ul-Fiqh is the means to that end result. Fiqh is commonly translated as Islamic jurisprudence. These derived rulings or laws cover seven different subjects of life:

1. Rulings related to worship (prayer, fasting, pilgrimage, etc.)
2. Rulings related to family (marriage, divorce, etc.)
3. Rulings related to action of people (buying, selling, business transactions, etc.)
4. Rulings related to duties of the ruler (i.e. Islamic politics)
5. Rulings related to criminal law
6. Rulings related to a Muslim country and it’s relationship/behavior with other countries
7. Rulings related to manners (akhlaq) and modesty

The extracted rulings related to actions fall into one of five levels:
1. Wajib – Obligatory. The one who does it will be rewarded while the one who avoids it will be punished.
2. Haraam – Forbidden. The one who does it will be punished while the one who avoids it will be rewarded.
3. Mandub – Recommended. The one who does it will be rewarded while the one who avoids it will not be           punished. 
4. Makruh – Disliked. The one who does it will not be punished while the one who avoids it will be rewarded.
5. Mubah – Allowed. The one who does it or avoids it will neither be rewarded nor punished. So there is no          reward or punishment for doing or not doing actions of this level.

Because Fiqh is the result of all of the other Islamic sciences, it is usually the main focus of study in the beginning for students of knowledge after Aqeedah. Particularly the rulings related to worship should be studied and practiced immediately. The one who is well versed in Fiqh is better than the one who is not, even if he is well versed in the other sciences. This is because knowing and understanding Fiqh means that the person understands the commandments of Allah and how to apply them in his daily life. Such a person is able to live a life in accordance to the Will of Allah and fulfill his purpose of life, which is the worship of Allah with complete submission to His commandments and prohibitions. 

Differences of Opinion

It is also important to note that Fiqh is flexible in the sense that there can result valid differences of opinions amongst scholars on various issues. As for why these differences occurred, then this is a topic which is usually studied under Usul-ul-Fiqh. Due to these differences, in the Sunni sect there are four main schools of thought (madhahib): Hanafi, Maliki, Shafi’i and Hanbali. These schools were established and popularized by the students of the classical jurists, after whom these schools are named, who taught them. Originally there were many more schools of thought but most of them died out. There are other schools of thought in existence and practiced throughout the Muslim world but are not as much popular as the four mentioned above.

Since in the beginning it is difficult for a beginner student of knowledge to determine who is right or wrong and who to follow and not follow, it is recommended for such a student to follow a teacher that he trusts in all his affairs even if it means following a particular school of thought (madhhab). Then as his knowledge grows and the evidences from other schools of thought come to him, then he should follow the strongest proof wherever it may befall.

Shaykh Saalih al-Fawzaan said:

People fall into four categories:

The first category is those who are able to make ijtihaad in absolute terms, by referring directly to the Quran and Sunnah and deriving rulings from them, and they do not follow any other scholars (taqleed).

This is the highest status, but this only applies to the one who fulfils the known conditions of ijtihaad, by having knowledge of the Book of Allah and the Sunnah of the Messenger of Allah ﷺ, and by having knowledge of Arabic in which the Quran was revealed, and by having knowledge of al-muhkam and al-mutashaabih (clear, unambiguous texts and ambiguous texts), al-naasikh wa’l-mansookh (texts which abrogate others and texts which are abrogated), al-mutlaq wa’l-muqayyad (texts with absolute meanings and texts with limited meanings), al-khaas wa’l-‘aam (texts with specific meanings and texts with general meanings). He should also have knowledge of how to derive rulings, meaning that he should be qualified. Such a person may engage in ijtihaad. This category includes people like the four imams – Abu Haneefah, Maalik, al-Shaafa’i and Ahmad – as well as Sufyaan al-Thawri and al-Awzaa’i. To these people Allah gave the ability to engage in ijtihaad.

The second category is those who cannot engage in ijtihaad in absolute terms, but they are able to weigh up the opinions of scholars and determine which is more correct, because of their knowledge of which opinions are based on evidence and which are not.
Such a person must follow that for which there is evidence, and shun that which goes against the evidence. This action is called tarjeeh (weighing up what is more correct) and is also known as al-ijtihaad al-madhhabi (ijtihaad based on the study of different views).

The third category is those who cannot engage in tarjeeh. Such a person is regarded as one of the muqallideen (those who follow other scholars), but if he knows that some opinion has no supporting evidence then he does not follow it. But so long as he does not know and it is not clear to him that it is contrary to the evidence, there is nothing wrong with him imitating and following the opinions of the trustworthy scholars.

The fourth category is the one who is unable to do any of the above; neither ijtihaad in an absolute sense nor weighing what is more correct nor following a specific madhhab, such as the ordinary Muslim, for example.

Such a person has to ask the people of knowledge, as Allah says: “So ask of those who know the Scripture, if you know not” [al-Nahl 16:43]. So he should ask the one who be believes is most trustworthy and the scholar in whom he has the greatest confidence, of those whose knowledge and actions he trusts, and follow his fatwa.

These are the categories of people with regard to this issue.

What a person should do is know what level he is at, and he should not put himself in a higher position than he deserves. Indeed, the matter is more serious than that. He should fear Allah, because it is the matter of halaal (permissible) and haraam, of Paradise and Hell, so he should not indulge in matters that he does not have the knowledge and skill to deal with.

Islamqa.com, 113687

And Shaykh Uthaymeen said:

The one who has no knowledge and no ability to engage in ijtihaad must ask the scholars, because Allah says: “So ask the people of the Reminder if you do not know” [al-Anbiya’ 21:7]. Allah does not enjoin us to ask them except for the purpose of following their opinions. This is taqleed (following). But with regard to taqleed what is forbidden is adhering to a specific madhhab by following it in all cases and believing that this is the way to Allah, so one follows it even if it goes against the evidence.

But the one who has the ability to work things out (ijtihaad), such as the seeker of knowledge who has an abundant share of knowledge may engage in ijtihaad on the basis of the evidence, and follow the one who he thinks is correct, or is most likely to be correct.

As for the ordinary Muslim and the beginner seeker of knowledge, they should strive to follow the one who they think is closer to the truth, because of his abundant knowledge, strong religious commitment and piety.
Islamqa.com, 113687

Usually, Fiqh is learned in the following order:
1) Learn the rulings without the evidence. This is so to strengthen the fundamentals.
2) Learn the evidence of the rulings
3) Rationalize the rulings
4) Compare rulings to other schools of thought