Urgent! Cutting Music Help!

hi dance teacher reddit. i need your help! i have never cut music before and i have no clue where to start. i have garageband and i’m ready to use it but i do not know how to get music onto garageband to cut. i was trying at first to find an app that would convert youtube video links into an audio file but it never works. i have to get music cut for the holidays and any advice would be appreciated! thank you! xx