It depends on the sentence. For example: I heard your mom's going to Germany. A lot of moms will be at the party. Basically, 'mom's' is another way of saying 'mom is' and 'moms' is the plural of...
tell someone, like a best friend or a guidance counselor, it can be hard to tell, but abuse is serious. If you trust your mom, tell her your going to tell someone just incase, so she knows. Good Luck!