You can earn coins by sharing referral link to your friends. For each referral deposit for doubling, you will receive 15% of the deposit amount.
Example: https://justdouble.info/?r=1AyUUKTx17UX4nTEMQb2Dmn2eqfHmBC8U1 . It is recommended that you provide multiple coin type addresses. The commission will be paid to provided address only. If the person referred by you deposit in Bitcoin, you will receive 15% in Bitcoin. If Bitcoin address for commission payout not available, it will be forfeited.