Close the shutters. Measure the width of the opening the shutter-T post is going to cover. Measure the height of the window to determine how long the T-post needs to be.
Hold the T-post in the desired location. Open the shutters again so they are out of the way during the T-post installation. Mark where the pre-drilled holes are on the T-post onto the window frame. Drill pilot holes in those locations.
Attach the T-post to the window frame with the flathead 6-by-1.5-inch screws included in its assembly kit. Close the shutters once again, setting their edges behind the T-post.
Cover the screw heads with a button plug from the assembly kit. Not all manufacturers include plugs in their kits.