Coins could be purchased on Cuddle by going to the "Account" tab - "My Wallet". You could also earn coins by collecting "Check-In Rewards".
Stars only represent the all-time total value of gifts received from other users.
Star count is only a number and can not be used for anything. E.g. If the all-time total gifts received value of a user is x coin(s), then he/she has the same amount of (which equals to x) all-time total stars.
Diamonds also represent the value of gifts received from other users.
The coin value of gifts received from other users will be exchanged to diamonds at a certain rate.
Diamonds can be used to cash out.
Crystals only represent the account's activity for tasks on Cuddle.
Crystals can be obtained by completing check-in and daily tasks.
Users can send crystal gifts to others in the live room with crystals. Users who receive crystal gifts will get a certain amount of cuddle points to get leveled up.