Do I have to sand to pain ? Help

[locomoco19]

My stair case is wood, it's already painted.
My question is can I just paint on top of the paint that's already there? Or do I need to sand it?

Also I have a (hideous) brown fireplace, which was supposed to get stripped out but due to current situation that can't happen now. So for the time being I thought I will paint it, again do I need to sand it down first?

In the middle of the fireplace there's gloss finish tiles, can I directly paint on that? Am guessing I will need specific paint ?

Sanding down surfaces will help paint adhere, but after sanding down my skirting boards with about 50 years worth of gloss on them, it’s clear some people aren’t bothered 😂 I would think you’d need specific paint to adhere to a glossy tile, I know you can buy specific tile paint but I’ve not used it before.

You can use a primer like ZINSSER B-I-N SHELLAC-BASED PRIMER SEALER - just sand down any drips or lumps first.