What do politicians do?

I do not have much familiarity with politics other than being aware of how politicians are portrayed in the public, including a bunch of jokes made about them.

So, in reality, what do politicians do (and, does anyone know)?

Do politicians simply sometimes favor certain groups of people and their interests over others, perhaps allocating funds to given projects or causes, over others, or, do they do other stuff?

What are their roles?

Thanks.