There are 2 places you can find out your order number.
Order Confirmation Email
When you place an order, you are automatically sent an email from us, confirming it. The order number (as well as how to contact the store) is on there:
Orders page (if you have a Storenvy account)
If you have a Storenvy account (specifically, if you had the account before placing the order and used it to make the order) you can also look up your order number on your "Orders Page