First, before you jump in to getting certified, there are a few things you should know. If you have a small farm that sells less than $5,000 each year, certification is not mandatory in order to use the organic label. However, if you sell commercially (as in to retailers, rather than directly to consumers) or sell more than $5,000 annually, you have to become certified in order to use the USDA Certified Organic label.
To get certified, you have to practice organic standards, as published by the USDA. You have to either have three years of records or follow a three year transition plan so that you have records indicating no harmful or prohibited chemicals have been used on the land for that time. Even when raising livestock, you have to prove what has been put into the land for the previous three years.
The next step is an inspection by a certifying agent. Each agent charges for inspection services, with fees varying from one agent to the next and one region to the next. The agent will ask to see your organic operating plan, to see how you plan to continue following USDA guidelines. Once the initial inspection is done and your operation approved, you can use that USDA organic label. Just keep in mind, you'll need a yearly inspection going forward.
For those who don't want to incur the expense or time involved in becoming USDA certified, there are private organizations that also offer organic certification. Many follow the same guidelines as the USDA, but charge less for gaining certification through their organization.