I just found out about this recently. aka 5 minutes ago
Beauty Bank Points
You receive one point for every dollar spent on merchandise at Sephora.com or in Sephora retail stores. Every time you accumulate 100 points in your Beauty Bank, you can choose 1 Beauty Insider Deluxe Sample with your purchase. When you choose your Deluxe Sample, 100 points are deducted from your Beauty Bank balance. Beauty Bank points have no cash value and can only be redeemed for samples.
When purchasing items at our retail locations, be sure to let our Cast Members know that you are a Beauty Insider by referencing your registered email address or presenting your Beauty Insider card. When you log into your account on Sephora.com and place your order, points are accrued automatically.
To view your Beauty Bank balance online, simply log in to your Sephora.com account. On the My Account page, your balance is located within the black stripe to the right of the words "Beauty Insider."
I have 54 points
ETA: I didn't know about this one either
Beauty Insider Card
You do not need a Beauty Insider card to shop at Sephora.com or to accumulate points in your Beauty Bank. If you would like a Beauty Insider card, one can be picked up at a Sephora retail store. Please provide your registered email address to the cast member at the store so that they can link your Sephora.com account to a Beauty Insider card. Beauty Insider cards are not available by mail and are not required or used for online purchases. When shopping at Sephora.com your registered email address is all that is needed to insure your online purchase is automatically added to your Beauty Bank.
If you have misplaced you Beauty Insider card, you can simply pick up a new one on your next store visit. The Cast Member can pull up your registration information using the email address you provided and link your account to a new card number with no delay. Please also keep in mind that Beauty Insider cards are not needed to shop at Sephora.com.