what is self control?

Is it something like a work to do? 

or a daily task that we have to do definitely ?

This is not like that. There is a word i.e., "instant gratification" that what we need and here is the requirement came of self control. 

why do we need of instant gratification?

Here is a lack of patience that led us to failure. There is a study called Marshmello study where children are given marshmello to eat and asked to wait for 15 minutes and if they do so they will be given another one marshmello or otherwise they may eat that one. 

Some have not that level of patience they finished that one marshmello. Those who wait they get another or we can say those who wait they get bigger result.

So the conclusion is the difference between want and need is self control.