it just means you dont give either way. when you say it you fling your hand either up or down, depending on the context in which you are saying it. eh! said as a short sound means you dont care, but if you enlongate it and say it more slowly with a downwards action of the hand it generally means you can't be bothered to do something (whatever the person asked you about)
male: do you want to have sex?
mother:are you going to go to work on your homework project tonight?