Like everyone else here, I have spent hours trying to figure this out, looking for the Devices category in the Sidebar and then Remote. Nothing worked, until I finally figured it out. I think this method is foolproof...:-)
1. Open iTunes and make sure it is connected to your home network.
2. Go to "View" on the top bar and then "Show Sidebar". You should see Music, Films, etc, BUT YOU WILL NOT SEE ANY 'DEVICES', not just yet.
3. Now, go to your iPad/iPhone, make sure it is connected to the SAME home network. Open the Remote app on your iPad/iPhone.
4. Go to 'Add an iTunes Library'. You will get a four-digit code
5. Now, look at the sidebar. Now suddenly you will you see your iPad, under the newly-appeared 'Device' category, listed as "(Name's) iPad"
6. Click on this new iPad icon in the sidebar. Four boxes appear in iTunes for you to enter the code from the iPad
Done!
The mystery is that your iPad/iPhone does not appear in Devices UNTIL you 'ping' iTunes requesting to control it remotely.
I also had firewall problems with McAffee. If the above doesn't work, TURN OFF all your firewalls and try again. If that solves the problem, you need to open a port on Mcaffee for access from devices on your network.