You have to save the icon after you design it, then long press** on the screen and select widgets (I know, it's not a widget). Then select simple text, 1x1. Then select the icon you saved. When you get to this step, you'll see the launch options as well to pick the app to launch.
**Might not have to long press...I dunno what launcher you're running and what OS. Just do whatever you do to place a widget on the screen. lol