Good question!
Say you have 3 objects A,B, and C
All the combinations of 2 are AB,AC, and BC there are no others There are 3 combinations of 2 objects
The order that the objects are selected in is NOT important.
BUT
All the permutations of 2 are AB, BA, AC, CA, BC, and CB There are 6 pemutations of 2 objects
You see, with permutations the order is important!