I have a TI-83 Plus but they're probably pretty similar.
1)press the "y=" button (top left)
2)type the function in the form y=... for example y=x+3. (the x button is the one marked "x,T,theta,n" if you didn't know)
3)press "window" (top left of calculator)
4)Set the boundaries... for the example above, use Xmin=-10, Xmax=10, Xscl=1, Ymin=-10, Ymax=10, Yscl=1, Xres=1.
5)press "graph" (top right of calculator)
I hope it works for you