To access the Battles page, the first step is to click on Battles in the left side menu:

You will be presented with the Battles page. Click the Battle Invites button: 

Select one of the battle invites clicking on it. You can view the battle details on the left end side, write a screen message which will appear on screen when the battle starts and either decline or accept the battle invite by clicking the Cross button (Decline) or the Check button (Accept):

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