When you want to register a trademark or copyright, you need to fill out an application form. When you send the application form to the Trademark or Copyright Office, that is called a "submission." They charge you a fee for each submission you send them.
Here is the link to the trademark submission forms: Trademark Electronic Application System (TEAS) Home Page
You will probably want the first one, INITIAL APPLICATION FORM. When you click on that link, you will have two options. Read through the info. One is the standard form, which will cost $325 to submit. The other is the Plus form, which is $275 to submit, but requires you to be able to provide more detailed info when you are filling out the form.
The standard form really isn't that difficult to fill out. The directions are pretty good and explains everything as you go. But if at any point you don't feel comfortable about it, look into using a local attorney or an online legal service to help you out. They may charge more, but it may give you some peace of mind.