While the trap bar is generally thought of as a tool for lower-body work, it can also work well for pressing movements. Due to the handle angle, it serves as a great shoulder and elbow-safe alternative to barbell pressing.
For overhead pressing, it works best to start with the bar on the pins in a power rack and perform each rep from a dead stop. The pins should be set anywhere from your traps to the top of your head, depending on your shoulder mobility and how you like doing your presses.
Trap Bar Shoulder Press
If you want to use more leg drive and turn it into a push press, just set the pins a little lower.
Trap Bar Push Press
One nice thing about this is that you don't have to worry about moving your head out of the way of the bar like you do with most overhead press variations.