Along with your Statement of Use, you must provide to the USPTO:
(1) a filing fee for each class of goods or services, and
(2) a specimen showing use of the trademark for each class of goods or services that you originally selected. Your trademark can only be registered in those classes and those goods or services as to which you can prove actual use.
Your Statement of Use includes a sworn statement signed by you (or someone authorized to sign for you), attesting to the use of your mark in commerce.