1996 Jeep Laredo Why won't my 96 Grand Jeep Cherokee Laredo

I had just driven 15 miles with no previous problems when I came out of a store to get back into my Jeep and it wouldnt start. I was only in store for 10 mins or less.
When I turn the key to battery only position all electrical devices fuction properly and strong. When I turn the key fully to start the vehicle nothing. No noise, engine does not attempt to turn over, but all electirical devices still turn on and function properly. Blower to heat kicks on also.
I tried to jump start the battery a couple times, once for over 10 minutes, but that did not work. I checked for good connection to the battery terminals, those checked clean and tight.
What should I look for next? How do I check the starter, or the starter solenoid? Please give details on where the things I might check are located. I am not very familiar with a lot of the mechanics of an auto, but I can figure it out myself if pointed in the right direction. I recently changed a water pump on this vehicle m