Quant and kentucky derby

Boxed Trifecta - must pick the top 3 horses out of 20 in any order. Do I use combination formula to get 1,140 possible combinations? Regular Trifecta - must pick the top 3 horses in order out of 20. Do I use permutation to get 6,840 possibilities? I’m a little confused on this because I’m not just selecting 3 horses, in one scenario i’m picking the top 3 but in any order in another I’m picking the top 3 in order. Can someone explain ?