How to determine subgroups and generators

Hello folks!

I'm new to this forum and I just want everyone to help me =)

In our Abstract Algebra class, we are to find for the subgroup(s) of this group:

G = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14} (this is mod 15)

I already searched the net and found out that there are trivial and non-trivial subgroups for this group... But still, I don't know how to determine those subgroups.

One more thing is how to get the generators of the group:

G = {0,1,2,3,4,5,6,7,8,9} (this is mod 10)

I don't know what generators are :(

Please do help me...