Now that you have some pictures and have an idea of what you will have to charge for shipping, the next thing to do is to create an eBay (and possibly PayPal) account and write a description. You will want to register for a personal eBay account unless you are going to be selling a large quantity of items on a regular basis. I would also recommend applying for a PayPal account; this will allow you to allow people to use credit cards or transfer funds from a bank account rather than pay you directly. It does cost 30 cents plus 2.9% to accept PayPal transactions, but in my experience, 95+ percent of people using eBay will pay with PayPal, you will in most cases be better off
If you are knowledgeable about what you are selling, you might be able to write a description, with little or no research. If not, you will have to do some searches. It is the Internet and no one will care if you "Borrow" another person's description, just be extra careful if you do, that everything that is said applies to what you are selling. 90% of the time I have found that I don't have to do any research outside of eBay, but you should be prepared to, especially if it is a rare item. Be very descriptive, but if you are selling an Xbox One, well everyone knows what that is, don't they?