Capes can be equipped with the
/cape equip "capename"
command
Capes can be unequipped (will reset you to your mojang provided cape)
/cape unequip
Commands have Luckperm nodes for each cape individually so you can assign them to your server's different ranks, or hand them to various users who won an event or did some sort of contribution for your community server.
All capes are useable by all users by default (in singleplayer or on a server that doesn't have Luckperms set up)
The mod is required by both server and clients to work as serverside synchronises the capes across the server, and the clientside does the rendering