First of all, read this link from Ebay's help pages :
http://cgi6.ebay.com/ws/eBayISAPI.dll?MfcISAPICommand=S...=seller+requirements
To check if you've create a seller's acct (which you must have, judjing by the wording of Ebay's message) go to your 'my ebay' page...on the left there will be a section that says 'all selling' with sold, unsold, etc below it. If you have no selling acct it will just show as a link that says 'start selling now'.