If you are listed with a Realtor, contact them to add your property to Trulia. If you are looking to add your property on your own as a For Sale By Owner, only Realtors can add listings to Trulia at this time.
Selling on your own can present many challenges and safety concerns. At some point you may want to interview a couple of Realtors. There should be no fee to meet with them and commissions are negotiable.
Best of luck to you.