First, go to ebay.com and register a username. Before you finalize your name, though, be sure to think it through. You might not want to pick the username that you commonly use on the Internet. People may be able to search and see other things you've posted online if you make your everyday username available. It might not necessarily be a concern, but it is something to consider. Alternatively, it might be smart to pick a name that reflects the type of business or products you want to sell. "Jane Doe's Antique Glassware" is just one example. eBay also allows you to change your uername at any time, so whatever decision you make, know that it does not have to be final. If you change your mind or your business later, you can alter your name accordingly (and it does not affect your feedback or reputation).
Secondly, you need to set up your seller account on eBay. Click on eBay's selling tab on the eBay website. You will have to fill in information such as the mailing address for your "store" and your PayPal information. You may also need to include bank account information. eBay does not charge you to sign up, but there are fees associated with selling items. Your listing fees and final value fees will be charged monthly to your bank account or credit card unless you specify otherwise. Either way, eBay has to have this information on file.
Next, prepare all of your items for sale. If the items are new, they should have everything that they originally came with included. If they are used, make sure to note anything that's missing or damaged. You may want to clean the used items as best you can. You will also need to specify what overall condition the items are in. Take pictures of your items and write up detailed descriptions of each one (make sure to list damages, discolorations, missing parts, etc). There should be both a picture and matching description of all defects on used items. If you home has smokers or pets, note these facts in your items' descriptions, as it can affect buyers with allergies.
Finally, it is time to list your items. Under eBay's selling tab, you should see a tab to list new auctions. Fill in the keywords to your auction, and on the next pages you will be asked to add your item description, photos, and starting auction price. Once this is all complete, submit your auction.
That's all it takes. You can now go on listing more items for sale and watch the bids come in!