I want to create a Gui that lets a player follow another player through a universe. How would I find the UserId of a player from their username? Apocalypse Rising has an example of what I am looking for. http://www.roblox.com/games/1600503/Apocalypse-Rising
What your looking for is this.
game.Players:GetUserIdFromNameAsync()
in the () put the username inside of it, and it will return the UserID.
Depending on where the gui is, you can simply just do script.Parent.Parent.Parent.UserId (Or where the Parent.UserId ends) until you get the actual player. Or, use game.Players.LocalPlayer.UserId Should get the UserId.