The trademaking process goes a little something like this...
You come up with a phrase that you want to trademark.
You go to this site for the U.S. patent and trademark office.
You click on the trademark link in the sidebar. You can file online or on paper forms that you mail in.
You research the current trademarks to make sure that the phrase is not already in use. (They have reseraching tools for this.)
You then decide what you want your trademark to appear on. (You have to make sure to get all the categories of goods that you want included in your trademark, otherwise someone can use your trademark on goods that weren't covered in your categories, and you have no rights to it.) You pay a fee for each category, and the overall trademark.
Then you submit it to the office, they assign someone to make sure you are the first to pursue a trademark on it, and eventually they get back to you letting you know whether or not you get it. If you're not the first to pursue it, they get to keep your money, so that researching thing pays off. And if you're the first, then it's yours.
And that's how it's done.
Its not hard at all, just a little bit costly, and it's maddening to wait on the approval.
Fortunately, we were the first to think of trademarking, "I want to like you but..." But we filed for two trademarks to prevent knockoffs... It was an expensive, but strategic decision.
And so there you have it!