OWWWCCHHH!!! This is very PAINFUL how do I get rid of my CANKER SORE?

Yeah I am getting a canker sore and i am younger then ten and i don't know if i should be having them but if I should what are some ways to cure them it happened to me on the right of my gums also in the center it was yellowish and it was not bleeding but now its in my left gums and its bleeding a lot what are some ways to cure it?