Hi there pokrman 101,
Welcome to Salehoo!
Payment terms will vary across dropshippers, but most will either (a) require you to have credit in your account or (b) pay for the item at the same time as you send payment instructions.
For example, MK Enterprise have both of these options. When you make a sale on eBay you can just go into MK Enterprise, select the product, put it in your shopping cart and if you have money in your account, the amount will be taken out of that. If you don't have a credit, you'll be asked to enter your payment information to pay then. Then you add the buyer's shipping details and MK Enterprise will then ship the item to the buyer.
You can upload your logo and everything to the site so that your branding and sender information is on the box. (This is known as 'blind dropshipping' - the parcel looks like it comes from you rather than the dropshipper).
Different dropshippers will vary as regards to buyer address info - some will require you to email them with the buyer's address when you make a sale, rather than doing the shopping cart option like MK Enterprise. But when you sign up for account, they'll let you know who you need to contact.
Hope this clears things up a bit!
Feel free to ask more questions as you look around :)