Understand The Difference Between Permutation And Combination Permuation/Combination Problem??? Please Help.?

Permuation/Combination problem??? Please help.? - understand the difference between permutation and combination

Yes, I am very confused, to say the difference between permutations and combinations, and since I do not really understand how to solve this problem:

Sue loves to read mystery books and manuals auto repair. During a visit to the library, is 9 pounds secrets and 3 new automotive repair manuals. It takes 4 of these books. Find the number of different groups of 4 pounds of Sue can borrow if:
(Parts)
a. they are all the secret pounds
b. are exactly 2 pounds of mystery
c. 1, a single book is mustery
d. All are car repair manuals

I would be glad if you return to me as soon as possible, thank you!