You can invite new players to the game by sending them your referral code, which can be found by tapping the referral icon on the home screen:



New players (anyone who has not reached Planet 5 or XP level 5 yet) will see an option to enter your code on their home screen:





The new player will then see their progress on the quests by tapping the same icon on the homepage:



You will see their progress (along with anyone else you refer) under the 'Progress' tab, and you will both earn rewards for milestones reached: