Well, here's the basics:
You tell them to do /b b <move>.
Then you tell them to do /b d Water, Fire, Earth, Air, Chi (whatever element they are).
You then tell them to choose whatever move they want.
Then when they binded a move to a slot, you then ask them, "See how there are 9 boxes/squares on the bottom?"
If they respond with a 'yes', then you reply with "Each one of those holds 1 move. So you go from 1-9 on your keyboard. You can only hold 9 moves in total."
If they respond with a 'no' then you tell them to press from 1 - 9 on their keyboard, and tell them each one holds 1 move. (I suggest you should download BendingBoard for more self-explanatory details)
After they have binded 9 moves, you tell them to do /b h <move they have>.
They should be able to learn how to use the moves by themselves. If they're having trouble with a move, you could help them out.