MJWL gives good advice.
When your customer pays you will be notified by Paypal that you can ship. Paypal also gives you a discount on many shipping services (from 5%-17%) so you can print a label from there, even though the payment is being Held against your good service.
Most parcel services include Confirmation of Delivery. If your dress sells for more* than $750, or if it makes you feel more secure, you can pay $1.50 for Signature Delivery.
*First, yay! Second, don't sell anything you can't afford to lose until the Hold is lifted and you have at least 10 Detailed Seller Ratings. Trust us on this?