Lay the fence post horizontal on the ground. Make a mark up from the bottom of each fence post at your desired depth. This will allow you to set all the fence posts at the same depth.
Slide the T-post driver over the fence post and stand the fence post upright at the location you wish to pound it in.
Pound in the T-post using an up-and-down motion on the T-post driver. Periodically check for level to ensure you are pounding the post in vertically.
Remove the T-post driver once the T-post reaches its pre-measured mark.