To get started, you can find your friends on Tunnel Town by launching the Game Center app.  Exit Tunnel Town and find the Game Center icon on your device, or launch Game Center from within Tunnel Town by tapping the “Buddies” icon in the game (the circle icon with two waving bunnies), then tap the Game Center icon at the bottom of the Buddy List screen.  With Game Center open, select ‘Requests’, then tap on ‘+’ to create a friend request, and enter your friend’s Game Center ID. Once they accept your request and install Tunnel Town (if they don't already have it), they will show up on your buddy list in Tunnel Town.  They will also appear in the Game Center app itself, under Games-->Tunnel Town.