When you follow a referral link, you must complete your first transaction. After that transaction is completed, you will see a bonus 100 DRIP waiting for you to withdraw at your next DRIP.
When someone else clicks your referral link, and completes their withdrawal, you can then check your available DRIPS, and you will see 100 extra drip tokens waiting for you.
Referral rewards do not expire! You can allow these to accumulate between epochs if you like.