Currently there isn’t a way to jailbreak an Apple TV 3. We don’t know when or if it will be able to be jailbroken.
You can stream content that is loaded into iTunes to an Apple TV but you need to convert it to make it compatible. There was a thread not to long ago on here regarding it but I cannot seem to find it.
Your other option is to return it to the store and get a different product. Unless you have, or intend to buy more apple computers, tablets, and phones you won’t get much value from the ATV (without JB). There are other better products out there.
It does appear that all hope has been abandoned for ATV3 to be jailbroken, ever.