Start a game with your favorite seed.(You can build something there if you like.)
Tell your friend to come to your house. (You need to use the same wifi to do multiplayer.)
Tell your friend to to click join game. (You have to click the button that says server is invisible first to make the server visible. If its already visible, move on.)
He will join your game. (be careful, he might kill you and steal your house)
MULTIPLAYER BATTLE STARTS!!!