You can have friends in the game. Friends can send gifts to each other in the form of one Friendship Point every day.
You can purchase Friendship Gift Boxes using them. These boxes give you tons of gold you might need for upgrading cards.
To access your friends list, tap on the community button in the home screen.
Community Button
It should take you to a screen like this:
This shows your friends. To the right, you can find options to send them the gift, or to receive one from them (if they’ve sent the gift to you).
In the next tab (second option at the top), you can add a friends by entering their Nickname or UID or simply by adding one from the “Recommended Friends” section:
Lastly, the third tab takes you to Incoming Requests - there, you can check which players have requested you to be a friend of them and you can either accept or decline their request.