QUESTON ON PUPPY MANGE?

ok so my mom was driving in the winn dixie parking lot when she noticed a animal on the ground. she thought it was a dead animal but cars kept going around it. so she pulled up next to it and saw that it was a very small puppy. she took it home and it wont do much. it just stays close to u and tries to cuddle up nxt to u. and it wont eat or drink. and it walks weird, like it ducks close to the ground. we think it is too young to be away from its mother or eat or drink water. the puppy also has bald spots on its back. the skin is its natural skin color and feels normal. just bald. i was wondering if it could be mange? also how do puppies get mange? and is it contagious to other dogs? (we have 4 dogs)