If you want to start a game with a friend, you must select the orange "Play" button, located at the bottom of the game's main screen, and then the "Classic Mode" option. Next, you will see the "Select your opponent" screen, in which you must enter your friend's username or the email address that they used to create their account. Once you do, you must click on their profile photo and again the "Play" button. That way the game will begin.
On the other hand, remember that you will have the possibility to invite friends to download the game through the "Invite friends" option in the "Games" tab. To do this, you must go to the section of the game represented by the icon of a list, located as the second option in the bottom bar of the screen. We invite you to read more about it in the article: "How can I invite a friend?"
If you are part of a team, you can also play the Tower Duel mode with your teammates. To learn more about how to play with your teammates, we invite you to visit the following article: "How do I play a Tower Duel with my teammates?"