QUESTION: How can I DJ with my Fast Track Pro setup?

I want to practice DJing, but my speakers are only the computer's speakers and some headphones. How can I set up a DJ setup with my speakers 1/8 input and my headphone 1/8 input. I do have a jack that turns a 1/8 into a 1/4.

edit: I am using VirtualDJ, and I have a mouse and keyboard. My speakers have 1 input.. like a headphone jack. And I also have headphones with one jack.