Click "Play" from the left-hand menu and select "Play" from the appearing menu.
This will take you to the play page, click "Custom:"
Click on the down arrow next to "Standard" to change the game type and select Doubles (Bughouse):
Your partner will default to a random person. Click on "Random" under "Partner" to type the username of the member you want to partner with.
Once you've selected your partner, click on the green "Partner" button at the bottom of the screen to send the invite.
If the member you invited isn't responding, you can cancel the invite and try inviting someone else. Simply hover over "Waiting for Partner...," and it will change to "Cancel:"
You can play against a random opponent or choose your opponent by typing their username in the "Opponent" text box:
Once your partner accepts and you've decided on an opponent, click the "Play" button to start the game!
Check out this article to learn more about Bughouse: What is Bughouse?
How to unpartner
If you've accepted an invitation to partner with someone in a Bughouse game and want to cancel it, here's how you can unpartner that member:
Click "Play" from the left-hand menu and select "Play" from the appearing menu.
This will take you to the play page, click "Custom:"
Click on "Standard" to change the game type and select "Doubles (Bughouse):"
You will see your partner's username here. To cancel, simply click the icon
next to it: