Playing Fortnite with your friends is easy thanks to the social panel that can be found both in the Epic Games Launcher and within Fortnite itself. Once opened, click the plus button at the top of the panel and enter your friends email or display name.
Once the invite is sent, your friend will see a request in the "Invitations" section of their social panel. Hitting the "Accept" button will place you, and your friend, in each other’s Friends list.
Inviting your friends to a game you're in is just as simple as joining. Once you are in a game open the social panel, click on your friend and choose "Invite to Game" from the dropdown. You’ll notice that the invite and join options may both be there if your friend is already in a game. Now that you have a friend you can see if they are playing Fortnite and join their game. If your friend is playing you will see the Fortnite logo next to their name along with a brief description of the game they are in. Just click on your friend and open the dropdown to the right of their name. Clicking on the Join Game button will launch you directly into their game.