I have an idea that will make me a millionaire. How do I patent it without telling anyone?
I don't have money or the smarts to do it either, so keep that in mind.
Ideas per se aren't patentable. Nor are they worth very much in and of themselves. To be patentable, you need to have conceived and reduced to practice some implementation of whatever idea you have in your head.
To put things in context, it is one thing to say, "I've thought of a perpetual motion machine that will make me a millionaire." It is quite another to reduce that idea to practice, either literally or constructively, i.e., by making the device, or describing it in a patent application such that one of ordinary skill in the art could make it without undue experimentation.
That said, if you have specific questions about the U.S. patent system please do not hesitate to ask.