Open up the material editor (m), select a slot (one of the grey balls), next to diffuse click the lil square button, then choose bitmap, then browse and select whatever texture you have made, then click the asssign button, its the one with a kinda arrow on it, then click the show button, the one with the blue and white checked square

your texture should now show up

try looking in the manual??
.. or pressing F1 to get the help function up?

both EXCELLENT methods :D
unless you got a student version that didn't come with a manual of course, but we still get the help files.