I was wondering. I am more of the electronic side of computers and not too savvy on the programmer side. but I was wondering. If I had an LED light hooked up to a usb port, how could I program, in C++, to turn that LED on and off?

It depends on the device. You will need a specification, but most manufacturers don't release them.

What is your OS?

I recommend ditching C++ for something like that, and using a much lower-level language.

If you want to use C++, you will, as chrisname more or less said, need a few technical documents about your OS and the system it's running on.

-Albatross

I found something:
http://www.libusb.org/
http://libusb-win32.sourceforge.net/

I am not convinced about the hookup of an led directly to an usb cable that you could turn on and off.
I'll check my usb books.