Party Play is a feature available through the NookPhone. Party Play allows you to call your friends and allow for 4 residents to explore the island together.
You will be able to switch out who's the Leader, which is the person doing the stuff. (Crafting, Building, ect.) The other player(s) will be able to collect items and shake trees, but will be put in the recycling bin for collecting afterwards. (Remember that if you are a follower, and have collected items that you do not want the other players taking, make sure to switch to the leader to collect your items.)