Trulia could clarify this if they wanted, as you're not the first, nor the last, consumer to be confused by that section of the site, but for some reason, they aren't dealing with the confusion that is caused.
As Alan stated, Trulia does not accept for-sale-by-owner listings. They say that this is a means to cut down on spammers abusing the site.
I suggest that you post your home for sale on Zillow.com and Craigslist.com as their services are free. However; for the best marketing exposure on the Internet I suggest that you use the services of an experienced local real estate agent. They can get your home on numerous real estate websites to give your home maximum exposure to attract the largest amount of buyers looking for a home like yours.
Prudential Connecticut Realty
An Affiliate of Berkshire Hathaway HomeServices of New England