Established online retail sites such as Amazon and Ebay are a secure way to find buyers for your records. Another site, Discogs, caters specifically to those buying and selling vinyl and CD's.
To sell a record online, you must first create an account with the site of your choice and post a listing for your item. You should include a picture and short description of the record. After your item is sold, you must ship your record to the buyer. The site usually takes a percentage of the sale.