If you're ok with using the command line, I would install adb, the Android debugging bridge. It's reliable and simple to use, but may be a little off putting for new users.
You will need to enable developer options on your Nexus 7 by tapping 7 times on the Build Number item in Settings -> About Phone. This will enable a new option, Developer Options, from there enable USB debugging.
When you're connected via USB, with adb you can verify that adb can see your device with;
You should see the following;
* daemon not running. starting it now on port 5037 *
* daemon started successfully *
List of devices attached
Where XXXXX is an alpha numeric string unique to your device. If you don't see the string, you haven't configured adb correctly.
You will be able to transfer files to your device using adb push
adb push myfile /sdcard/
and get files off using adb pull
adb pull /sdcard/remotefile /home/username/