The fan belt don't work well. I am told the pulley

It is neither an easy or a difficult job. But if you believe you can, then, you will be able to fix it. It is just a matter of taking out the bolts holding the pulleys, and some dirt. However, if this is not your cup of tea, you can have it done by a mechanic.
If this is fix on time, you might stall in the middle of a
traffic due to overheated engines. Running overheated
will have serious consequences, like a cracked or warped engine block, destroying your engine.

it depends which pulley is going bad. idler or tensioner......