If a club is private, only the founder can invite new players to join the club. Anyone can invite someone to join a public club. 

To do so, tap on the friend you wish to invite. You can easily get to your friends list via the “Friends” button on the home screen.

Tap on “Invite to club” to send an invitation to your club. If you wish to remove the invitation, tap “Cancel club invite”. 

A club invitation will expire after 7 days if it is not responded to.