1. it means "from..to...", or between.. .for example : 那有差不多5~10个学生。
2. it means something what has appeared b4,it often means this in Chinese dictionary.
3. in written Chinese (especially in the talk between good friends), it often means "friendly",or just means nothing.(If u want to make urself look more lovely,u can use this,too. :P)
5. sometimes it means“ 声音延长” (I don't know how to express it in English :P).
(it always be used when the person wants to be more friendly or lovely-- just as I told u,but girls use it more often than boys do )
hope it helps :)