What should I do I just went on minecraft and someone told me to kill myself?

Report them

1. DON"T kill yourself
2. Report them

Stop play minecraft online!

This could very well be a source for a cringe video some time in the future. Close your eyes, exit minecraft, and don't acknowledge the existence of cyber bullying.

EITHER: follow their advice. Or ignore their advice.

I suggest you ignore it and report them. Some people tend to take online gaming far to seriously. You may wish to reconsider the servers you visit and people you game with. Another suggestion is to not follow the advice of people on the internet unless it seems legit and doesn't involve doing something that could affect you negatively.

Report them to a Mod or Server owner. If nothing gets done, then either use /ignore <player name> or find a different server to play on.