AFL coding consulting needed

Hello,

I am looking for someone who's proficient in AFL and can teach me coding principles.

example here

Buy = (H-L) < Ref(H-L,7);
BuyPrice = Close;
Sell = Close > Ref(H,-1);
SellPrice = Close;

I am getting syntax errors, but I don't understand why I am getting them?

Your job would be to teach me and explain what I am doing wrong here.

Thanks