DCS Noob - How to access in flight menus, help with comms

[Gyster]

I'm brand new to DCS, and have finally dialed in graphics settings that work for my setup (Pimax 8kx, Virpil MC3, VKB Gunfighter, i9-13900k @ 5.6 GHz, RTX 4090, 64GB DDR5 @ 6000, 2 TB Samsung 990 Pro).  I've been flying the instant action missions, and noticed that some of them require a menu response to select difficulty level, but I don't know how to bring up the menu, let alone make selections once the menu is displayed.  I imagine, there are other useful menus/items that one needs access to while flying.  Can anyone recommend basic DCS tutorials where I can learn these things?

I've spent quite a few hours over the last week watching videos, reading forums and articles, and posting questions to finally get graphics settings for all the layers of software (Pimax, Pimax XR, Open XR Toolkit, Quadviews, DCS) dialed in enough to make the game playable (thanks again edmuss).  I've also learned enough to get my controllers set up for the very basic commands.  I've also been watching videos and reading articles to learn the DCS BF-109 K4.  I still need to learn how to get the most out of my controllers - I need to avoid using the keyboard because of VR (thinking about using Voice Attack and need to learn how to use Joystick Gremlin for keyboard bindings).  Then there's comms - it seems most of what I've found so far assumes some pre-requisite knowledge that I don't have. 

I think my priorities at this stage should be learning about any in flight menus and comms.  Any suggestions on where to start?  Thanks for taking time to respond.