Click "New Game" above, near the top left side of the page. Read the instruction for inviting a new member on the left side of the 'New Game' page, where it says to put your friends email address in the 'opponent' field.
Do this for each of your friends. They will receive an email inviting them to the site to play a game with you. They will need to open their own account before they can play, however.
You might want to talk to them as well so they will know what's happening, especially if they're not familiar with your username here.