Land without a building can be sold with a mortgage, without a mortgage, for cash or by a quick claim deed. The land needs to be researched for no tax or liens against the property and that it is free and clear to be sold. The land will be deeded to the new owner.
Selling all real estate (houses,land) is virtually the same. List the property with an agent, the agent finds a buyer, and hopefully the buyer makes an offer to purchase.
Find a buyer. Sell the property. Transfer the title upon receipt of payment. Ensure property tax records and the deed are updated to reflect the new owner.
You have two options. You may sell it yourself which means advertising, showing the land and producing a contract to transfer ownership or you could list the land with a realtor that would do all that for a percentage of the selling price.