Bball defense help pweeze?

im 5'5 so pretty small and i sometimes guard taller like 5'9 players haha. im rlly good with defense and footwork-one of the best on my team and thats y im being scouted, but i dont know wat 2 do with my hands. my coach told me it didnt matter and just put them bak like how if ur telling someone u dont wanna fite and u put ur arms bak with hands spread out..like that. i also stay low alot, but im just wondering when to put your hands straight up(and not get fouled) and when to keep them back.