Please help me??? german shepherd puppy problems ?????? HELPPPPPPPPP?

i bought the puppy he is 9 months old to city rescue he is SUPER SKINNY and when you put the food for him he eats a little he is a picky eater he doesnt eat the jerky rewards and probably he wont eat dry fooddddddddddddd!!!!!!!!!! and he doesnt play like fetch catch the ball the chewy toys he doesnt play with bit WERID PLEASE HELPPPP MEEEEEEEE THANKS I REALLY APPRECIATE IT PLEASE I NEED AN ANSWER FROM AN EXPERT THAT CAN HEL ME THANKS :) ;)