It's difficult to "factor" a polynomial on a TI-84. But you can find the "roots" of a polynomial via a couple of different methods.

1. Graph the polynomial. The points where it crosses the x-axis are the "real roots" of the polynomial. Let's graph y=x^2+x-6 and you see it cross the x-axis at x=2 and x=-3. That means two of the factors are (x-2) and (x+3).

2. If it's a newer TI-84 Plus, it will have an APP (under the 'APP' key) named "PlySmlt2" which includes a polynomial root finder. You can use that to find the roots, and turn those into factors.