It should be really straightforward (just plug in the console's various connections, plug in the power, turn it on, wait for 30 seconds to a minute to make sure you're on the right screen then hold the Xbox button in then press the start/menu button). This should turn on Narrator and prompt you to select whether you want to keep it activated if memory serves.
Then just go through the setup process and you should be fine. If you have any issues post here and I'm sure it can be sorted.
Regards,
Sightless Kombat.
***If you wish to refer to me in @replies, use Sightless***