Pre-disc golf I made and threw my own boomerangs for a while, it's a lot of fun.
Grip it at the very tip of the "right" wing, with the top (most likely the painted) side towards you, the grip is mostly a pinch between your thumb and first two fingers.
Throw it vertically (tomahawk style) with LOTS OF SNAP and forward speed basically level away from you (if there is any wind position yourself so that it is coming toward your left shoulder, this helps to bring it back to you at the end of it's flight when it's losing energy).
The boomerang should go out and start looping to the left (CCW) turning from vertical to horizontal as it does. At the end it should be flying almost completely horizontally like a helicopter, then nicely hover down to you. This probably won't actually happen for a while but keep trying. It's sweet when you don't even have to move! Enjoy!