using apple tv without a wireless connection

AppleTV requires Ethernet, either wired or wireless, to at least to get it setup (per the manual) with iTunes content sync'd and access to protected content authorized. After that, you can use it without a network connection to view its local content on your TV. That is as long as you can do without features that require access to the Internet, like YouTube, theatrical trailers and iTunes top content lists and previews.

How are you connecting to the internet now?

the apple tv sync and stream using itunes
for that it needs to be connected to the network which the computer
with itunes is located on
that can be don using wifi if the computer already have wifi and is connected to a router it's pretty easy

other option is wired using an ethernet cable connected to a switch, hub or router along with the computer

to work it also needs to be connected to a tv
depending on if you tv have hdmi or only component
or both you have to get a hdmi cable and or component cable to connect
to the appletv

if no switch, router or hub is present at all the appletv needs to be connected
to the compuer as adhoc wifi or with a crossover ethernet cable to the ethernet connector on the computer people seem to be having mixed results doing it this way though
plus crossover ethernet cables should not exceed 6 meters

Do you have a router for the internet with an ethernet connection?

You NEED a local network connection between your computer and the AppleTV.

This can be wired or wireless.

Tell us what your set up is now.

AC

"Is there a way to just hook up the apple tv to the computer and transfer music and videos and then hook it up to the tv?"

you would need the tv connected at least temp unless you could navigate the menus blindly but after you could disconnect it from the pc and just use it without network but it would
remove ½ the usage of the atv which is streaming and youtube and later on rentals and internet pic sharing stuff

"Do I need to buy any extra cables besides what came in the box?"

yes unless you have a hdmi or component cable around already
which one depend on your tv
you dont seem to have investigated before buying it if you already have it
but make sure your tv support atv or it's money well thrown out the window