TeamConnect has a bunch of video tutorials on Vimeo to bring you up to speed on ATAK Training.
TeamConnect is a great, easy-to-use TAK Server service that is used by many commercial, state and local users. Even if you don’t sign up for TeamConnect, the video tutorials are definitely worth a check. Its a pretty comprehensive set of lessons.
Here’s their basic intro video, but there are about 60 videos there.
Basic Function How-To from Team Connect on Vimeo.