Coefficients: Ok when you're going through your test, everything is marked out of 10. Some movements are awarded double marks, so next to the 10 you'll see a 2, these are the movements worth double. Usually the free walk is doubled and usually a transition (either trot-canter or trot-walk) has a coefficient.
Collectives: Are the marks at the bottom of your test sheet. Again, basic marks out of 10 but are doubled (coefficients ;)). These are basically for your riding (position, effectiveness of the aids etc.), horses paces (submission, willingness to go forward) etc. etc.