Legalities in performing music

[OompaLoompa]

I am trying to make sure I understand the legalities involved in performing music. I know you have to pay royalties if you want to record someone's copyrighted song and sell it, but what about performing in a public place? If I want to sing music written by someone else and I get paid for the performance, is that okay? What if I don't get paid?

Is there any difference legally between using a karaoke track or an eliminated track or having someone accompany me on piano?

I see people performing standards and other people's music all the time. Do they have to pay royalties for each song?