I am sorry to say, that all answers below are correct. You must have an agent submit the listing on your behalf. So I would say that if you do not have an agent already you may want to hire one and if you do have one hopefully they know about Trulia, actually you would be surprised on how many agents have never heard of this forum.
Basically your home has to be listed with a Realtor whether it is a direct feed via their brokerage;s website, or other syndicated sites. If your Realtor's brokerage does not direct feed into Trulia nor does he/she use other listing marketing tools which do, then your Realtor can submit the listing individually, see link below
Trulia Help Center > Submitting Listings to Trulia >
How can I post my listings on Trulia.com?
Your brokerage or Web site vendor may already submit listings to Trulia. If so please ask that your listing information be included in the data feeds they send to us. Otherwise, Trulia offers four easy ways for brokers and agents to submit listing information to Trulia directly:
The fastest option is to enter your listings one by one. Single Listing Submit is best for agents with small number of listings and who have a web site and your listing(s) should appear live on Trulia in about 36 hours.
The best option is to enter an xml data feed. This is best for large internet savvy brokers and the average time for listings to appear live on Trulia is about 72 hours.
The easiest option is to enter your listings web site address. This is best for medium sized brokers (50 listings or more) and the average time for listings to appear live on Trulia is about 2 weeks.