Are there special times when you shouldn't castle?

I was just wondering, sometimes I castle and sometimes I don't. But some people castle all the time. They win sometimes and sometimes they lose. Are there any special times when you're supposed to castle and speciel times when you're not? I am just a beginner so I don't really know the ropes. I was hoping someone could help me get when you should and when you shouldn't, because other wise I just don't get it. Thanks.

-thegirlnextdoor