Storage full

Hi. My Screen clicks out of facebook, I get messages saying my storage is full, I don't think I have a large amount of music or videos on my phone, took most of my apps off... I don't know what else to do? Phone doesn't work consistently, can't do things I want to with it .. I'm at wits end. I don't know how to use the iCloud...how do I fix this?? Thanks. Rmb