1)Location of an action, eg. tosho-kan de hon o yonde imasu>(I'm) reading a book in the library.
2)Manner or means, eg. Fune de ikimashou ka?>Shall we go by boat?
3)Materials used, eg. Kono Keiki wa, satou to tamago to gyuuniyuu de tsukurimasu> this cake is made of sugar, egg and milk.
4)Indicates superlatives within something>Sekai de ichiban shiawase ni suru kara, kekkon shiyou!> I'll make you the happiest in the world so let's marry!(thats taken directly from the course.....sorry)
5)Indicates condition> eg. Hitori dake de sunde imasu (I live just by myself)
Those are the main uses
1)Indicates a location and times, eg. Ginkou no mae ni imasu.> I'm in front of the bank
2)Indicates location of an action(ni indicates long-term action, de indicates short term action) eg. Resutoran ni tsutomete imasu> I'm working in a restaurant.
3)Indicates intervals, eg. Issshukan ni ichido tenisu o shimasu (I play tennis once a week)
4)Indicates movement, eg. Tokyo eki no mae de basu ni notte kudasai (Pease board the bus in front Tokyo station)
5)To go and do something---stem+ni+masu-base of verb, eg. Shokuji o tabe ni ikimasu ka? (Shall we go and eat lunch)
Using these concepts, you can understand other uses of ni, for example in change
eg. Taro-san isha ni natta> Taro became a doctor, even here, the concept of movement applies.
Hope that helped.