I would just leave the keybinds as default. For the most part I find them not that much more difficult than any other FPS. When you get into commanding AI and the like it gets pretty complicated and backwards, but if all you'd like to do is play simple infantryman stuff at first (I'd recommend hopping in the Armory and running around a bit) it's really not that bad.
Here's (in my opinion) what you need to know for standard pub or even clan gameplay:
WASD movement, pretty straightforward
Two different zoom levels (right mouse toggle and hold differences), aiming down sights
The wonders of the scroll wheel menu
Freelook w/ ALT key
Switching weapons with F
Stances - Z, X, and C
Basic understanding of ARMA's toggle controls - Doubletapping most commands (shift for run, alt for freelook, control for lowering weapon) vs. holding them down
How to read/open the map and compass (M and K keys)
Mods - If you choose to play with them. I'd hold back on doing too much with the gear system if you want to play online, as ACE (one of the most commonly used mods) really changes it. ACRE IMO is essential, but there are so clans that play without it.
I figure that's oversimplifying it, but do you want to play online or singleplayer predominately? If you want SP you'll need to learn a bit more and how to control the AI, but for MP I've found most open communities are happy to teach if you're willing to listen.
