My bunnies haven't started to moult yet, but they will in the next month or so.
The moult usually starts at the head end, and gradually works back along the body, with the bum bit being the last to go!
If you look at this pic of one of my bridge bunnies, you can see he is half way through moulting, and the moult line is clearly visible! They look a bit weird when they are half done!
It is usually a messy time when buns are shedding hair, as it ends up everywhere, and all over your clothes and house if they are indoor buns.
Brushing helps, as does hoovering if your bun doesn't mind the noise, but be careful not to suck up skin.
Mine are outdoor buns, and grow their thick coat for the winter, and then shed it in the spring, so yes, just once a year.