I'm a new homeowner and I've never dealt with tanks/pumps/water filteration before. This is a picture of my tank, but I noticed at the bottom of the tank, there is a very slow leak. Is this normal? What is this tank for? Is there some sort of maintenance I should be doing? I know nothing about this and I really need some help!

You will notice at the bottom of the tank there is a blue lid. That is where the water leakage is

There is also this thing which I have no clue what it is and the top of it has water in it (see 3rd picture below)

And there is this thing... I have no idea what this is