Help: Everybody knows the meaning of help (ayudar), but this word has others meaning unknow hardly for everybody, here they are:
1 - The first is of course "ayudar", but here in USA, they use a lot this construction: To help somebody out: I'm so busy with my new project, could you help me out with it?
2 - I can't help it: said when you are unable to stop doing something. I can't help laughing (No puedo evitar reirme). For example, if you are eating something that doesn't sit you well but you're eating anyway you say: I can't help it (No lo puedo evitar). (Sit well means "no sentarle/quedarle bien")
3 - Help yourself: used when telling someone to take as much food or drink as s/he wants. For instance, you are at your home and your roommate cooked something and it was letfover that he's not going to eat, so he may offer them to you saying: Help yourself! (Sirvete tu mismo)