What do trolls do in Minecraft?

They like to make you sad and frustrated. If you want to avoid being trolled i suggest you hide your house inside a mountain or somewhere it would never be found by a troll.

If you're making your own server, then start looking for plugins to help mitigate trolling. I don't care how nice you are… There's just going to be trolls that have their own agenda.

If you're looking to play minecraft on public servers then start jumping around servers. See what fits you and what protection they offer. Usually server communities (or ones I stuck with) have the right protection that I couldn't care if someone tried to steal/blow/etc. I end up getting my things back the way they were and trolls are gone. I haven't seen them much around lately.