No worries - I just looked around. This should help:

Setting up Home Sharing for Apple TV (2nd generation)

...unfortunately this shows how to do it in the older OS version on the ATV. The new system looks quite a bit different. Is there an all/tile in the new ATV menu that says "Computers" or something like that? If you'd try to access this, the ATV should ask you to enable Home Sharing first.