It may seem pretty simple to stick your home on the internet with a price and put a sign up in the yard. But really, there's more to it than that.
Your full-service realtor will take a look at similar homes in the area that are listed or have recently sold to compare to yours. They will also pull stats from the area, look at the property value of the neighbor's homes, and use all of this information to find the value of your home. This whole process is known as completing a Comparative Market Analysis (CMA) and helps the agent price your home effectively.
Once your realtor finds that pricing sweet-spot, they're half-way to listing your house.