Welcome, there aren't any familiarization courses at the moment but there are several videos that can help you. This is the familiarization course summarized in a short video: https://youtu.be/Pioba6xJ1Qw
For more advanced stuff you can refer to this formations guide: https://youtu.be/a483XQ2_5E8
We usually play Fridays and Saturdays starting at around 1900z - 2000z but feel free to join in progress at any time.
Its an open community so you don't have to take any courses to join. Just join when we're playing and listen to your Squad Leader/Fireteam Leader and he'll help you survive your first mission.
This will help you with the mods https://wiki.unitedoperations.net/wiki/ArmA_Getting_Started_Guide but feel free to ask on teamspeak or discord if you need further help.