Teeth whitening

I'm curious about teeth whitening treatment because my teeth are somewhat yellow.

First, I am curious if the procedure is painful or not.

I'm curious about how many times I need to undergo the procedure.

And during whitening treatment, it doesn't have a negative effect on the teeth, right? I'm very curious. Teeth can be whitened, but if there are harmful effects afterward, it's okay not to undergo whitening and just live without it.

I'm also curious about the approximate total cost of whitening.

And I saw an advertisement for whitening treatments done at home, not at the dentist. I'm curious if they are really effective. Wouldn't it be better to get it done at the dentist?