Each game in Pianola Play has its own unique link (web address, or URL).
Your club will send you a link for each game, or they may publish links to games on their website.
Click the link for the game you want to enter.
If you're already logged in to Pianola, you'll be taken straight to the "lobby" for the game, where you can select your partner and see announcements from the director:
Wait for the director to start the game, when you will be sent to your first table.