Major drills keeps asking me to add a sticker to a friends collection but I have absolutely have no idea how to do that, plus I just joined and I don't have any friends on here yet :/ lol
You buy a sticker, select it in your wardrobe, and click "Add to Friend's Collection" (or whatever the exact phrasing is). From there you can just type in a person's name, though I believe there are sticker forums - maybe in General Discussion or something? - if you need to do so moving forward.
Or you can put whatever cheap stickers you want on me, I don't really go for stickers but if it helps you...
the option doesn't even come up if you don't have any friends. I have sent you a friend request. Once you have at least one friend, you can stick anybody so you don't need to stick me.