If you want to enjoy some games without affecting your score or play against a friend with a much lower rating, you can play unrated games!
Hover your mouse over Play in the left menu and click on Play:
In the next menu, click Custom:
Make sure Rated is toggled off. This will make the game unrated, and no points will be gained or lost after the game is over:
Click Play to send out an unrated challenge!
Since fewer members play unrated games, it might take longer to find a match if you're not directly challenging a friend.
Mobile
Tap on New Game, choose More, and then select Custom
Toggle the Rated switch to off
Select your opponent by tapping Random and making your choice, or tap Play to find a match with another player who wants to play unrated games, or share the challenge link with a friend!