A madhhab usually refers to a schools of thought within fiqh, namely Hanafi, Shafiee, Hanbali and the Maaliki. Throughout history, there have been many, but these four are the only ones that have lasted till today. Now the question arises, do I have to follow one or should I make my own one up.
Well as the mass of the muslims are laymen, we would do the former. However, that does not mean that we are required to be very strict with the opinions of that madhhab as they may be more evidence for a certain act or not doing a certain act and we should follow that opinion accordingly, obviously given that this was postulated by a person of knowledge whom you trust.
When it comes to this topic, there are usually the two extremes where one is very strict to one school of thought and will not change their opinion even when there is more evidence for it. This is common amongst some hanafis in the west and in the subcontinent. This isn’t due to Imaam Abu Hanifa himself but with the followers of that school of thought, usually due to ignorance. Also, it goes to say that there isn’t a problem with people following different school of thought as even the sahaba had differing opinions amongst each other. The other extreme is that there are certain laymen who will refuse to follow a school of thought completely. This is wrong because laymen are not qualified to do ijtihad nor should they believe that they can reach this level, especially when some believe they can do this after reading a few articles online.
One may say that they follow their teacher, this is completely fine also, given that the teacher is well versed in fiqh. The main point is that we don’t take opinions based on our choice as that will lead us to choosing opinions that suit our whims and desires.