The United States Patent and Trademark Office, the government agency responsible for trademark registrations, provides up-to-date, comprehensive guides and toolkits:

It’s important to note that the USPTO is a SELF-FUNDED AGENCY.

This means they are incentivized to make every effort to help you through the application process. Well, it’s in their self-interest because they charge a flat fee for examining your application; poorly prepared applications cost them more time and resource.

Please do not ignore what they say “basics”. They are basics in the sense that you MUST KNOW THEM before applying for registration. It’s your first step toward legally securing one of your most valuable assets, your brands.