It is pretty straight forward. What don't you understand? You need to buy fieldrunners on the emunand of your system. Then edit some files with fbi. Transfer your emunand to the clean 3ds. These are just abbreviated steps but its pretty much what you have to do. You won't be able to finish the a9lh installation if you start it now though as the 11.1 update has blocked homebrew. Wait until it is updated