Setting up Teamspeak
Start Teamspeak and login on the server. Press on 'Settings' and go to 'Options' as seen on the picture here:

Click on 'Capture' and configure your push to talk button(I use an extra mouse button). This is a MUST!

Close this screen and got to 'Tools', click on 'Whisperlists'.

Click on 'New'
Press a hotkey at your choice (i recommend T Y U)
Now you have an empty whisperlist.

Drag the channels ASL, A1, A2, A3 that you can see in the first picture of this file into your whisperlist. Then press apply.

Do the same thing for the BSL, B1, B2 and B3 channels.

And lastly make one for the PL channel.

YOU ARE DONE!
What can you do now?
In your local channel you can press push to talk (shift). Only the members there hear you.
You can use T to talk to all in Alpha Squad
You can use Y to talk to all in Bravo Squad
You can use U to talk to Platoon lead