For this trick you need to first be able to do a normal backside 180 noseroll, it also helps if you have a reasonable degree of confidence balancing on the nose of the board and if you have backside 360s down as the movement is sort of similar.
1. Approach where you are going to do the trick with your arms would up to send you into the spin. Keep your eyes fixed on the point where you're going to pivot.
2. Unwind you arms to a normal position and put your weight onto the nose of the board, this will send you into the backside 180 pivot. Prepare yourself to pop when you reach 180 degrees. Try to look into the spin with your head to spot your landing.
3. Ok now you're at the critical point of the trick, you need to lift the board up of the ground, be that either by popping with your body or just sucking your legs up towards you. Twist the top half of your body into the final 180 degrees of the spin and the board should follow.
4. Now you should see your landing, and jus be able to float it in like a normal backside 360.
5. Land and crouch down to absorb the impact, quick check if your straight and correct it if necessary.
6. Make sure you leave one frame to ride out and look cool!
When I first started trying to learn this trick I treated it just like a flat ground backside 360 but just trying to leave the nose on the ground in the 1st half of the rotation. This trick takes a few goes to perfect but once you’ve got it down you can throw it in lots of places, off drops, off flat lips, and on the flat anywhere!