help needed for a friend! :)

[Powell123]

Hi, i sent your reply to him as you have gathered he has only started to learn this stuff 3 weeks ago, and is asking for help! so when i posted your reply to him all i got was ???? he still has not gotten any further...

i asked him what he does not understand about this.. his reply!

How to play a move on the board. e.g. enter 23 and for whoevers turn it is, if the move is valid, flip the number

What does that tell you about 8 and -8 and your index?