Why does my truck when i try to crank it it wont crank

First, do you have the proper key to the vehicle, programmed as needed? Second, you'll need to ensure you have a fully charged battery in the vehicle, one that is able to sustain a load. Next, you'll need to make sure you are in "park" or "neutral" -- and that the vehicle thinks it is also...a diagnostic tool will help indicate what transmission shift lever position is being seen.