To register a trademark with the U.S. Patent and Trademark Office (USPTO), you must prove that you are actively using your trademark to sell goods or sell or advertise services. In other words, you cannot register a trademark simply to tie up the rights to it. You must actually use it in commerce such as displaying it on products, packaging or other marketing materials.
This means if you originally applied to register a trademark on an "Intent-To-Use" basis (before you began using it in commerce) you must also file a Statement of Use to demonstrate that you are in fact using your trademark to sell goods and/or services. The Statement of Use form is required to complete the trademark registration process. You must file either a Statement of Use or a Request for Extension of Time to File A Statement of Use within 6 months of the issuance of your Notice of Allowance.