Did you receive an email message from AC similar to the one below?
$15 off your first purchase! When you open a free AliExpress account, you'll get a $15 coupon toward any purchase of $15 or more. Just be sure to sign up and then return to the Auctiva Sourcing tab to claim your coupon by 7/19, when the promotion will end.
Please be warned, and extremely careful. Alibaba.com is full of fraudulent sellers all over the world. Every Jack & Jill can become a seller on Alibab.com. 85% of these sellers required Moneygram or Western Union for payment. This is a big fraud.
AliExpress is a little bit different, because when a buyer makes a payment, it goes into an escrow account. A seller cannot touch or claim this money until a buyer receives orders, and satisfy the order is what was paid for.
You can read more about the escrow account in the link below.