IF you haven't logged off for a week or so you have to log out and then log back in. THEN go to classifieds and you should see the red button (I think it is red) to post an item for sale.
EXZI251, as I recall, you must have at least 10 posts before you can post an item for sale. Not sure if this is still the case. So you may not see the edit or post buttons until you get to at least 10 messages.
There is a help section on the HOME page of this site, as well as video tutorials that will help.