You don’t have to be in the same place as your friend to create a musical together; you can use musical.ly's duet function! To do a duet, select the musically of someone you follow (and who follows you back) and press on the "..." icon on the musical screen. Then, you simply need to press "start duet now!" and you can begin recording your duet. Again, just make sure that you and the person you wish to create a duet with already follow each other, or the app will not allow you to create a duet.