To post your home for sale - and it's FREE - you need to start on Zillow.com. Zillow and Trulia are the same company, so once it's posted on Zillow, it will sync to Trulia within 1 - 2 days. Owners need to type in their address, claim their home and then post it for sale.
BEWARE: Realtors pay monthly advertising fees to Zillow and Trulia in order to get leads from buyers and sellers. Because realtors pay monthly fees, they do appear on For Sale By Owner listings. Buyers who submit the Contact Form on your listing will be directed to the realtor on your listing - even though you have no contract with that realtor. Realtors can tell buyers that your home is NOT for sale because most realtors just check the MLS system and if your home is not in the MLS system - to a realtor it's not for sale.
To get around this, there are Flat Fee brokerages, Redfin, etc. You need to Google "flat fee brokers". Briefly, it means you can have your home listed in the MLS system for a small flat fee but you are 100% in charge of everything else. You will be required to pay a buyers broker a commission (about 3%) but you do save the other 3% by not listing with a full service broker. In a sense, once your home is listed in your local MLS system, realtors will be happy to show buyers your house.