From: The Imperial Palace.
GBS, there's an option in Preferences to take a screenshot automatically at the start of each game. Unfortunately, the resulting shots are sorta zoomed out, not as detailed as I like. So I just use FRAPS, the screen-capture utility. That's working fine for me. I imagine other (free) third-party screen-capture programs should work, too. There's always the good ol' PrtScrn button, followed by Paint/Gimp/Photoshop; that also works for me.
The supply numbers on the Unit Details screen would be self-explanatory to me, except that I'm still not sure whether intermediate HQs (Corps/Army for the Germans) play any role in supply distribution. The manual says no, but it seems like supply lines always travel to an HQ before they reach the ultimate destination of the combat unit. And the six fields on the screen you're asking about seem to suggest that Corps HQs are taking supply in and sending it out again.
Assuming I'm right that HQs play some role in directing supply, I read the stats as: Supply on hand are current stocks; Supply In requested is the supply request to OKH; Supply In is what in fact arrived; Lost is supply lost to interdiction (the manual does talk about that); Supply Out request is what combat units are requesting; Supply Out is what this unit actually sent along.
I would appreciate clarification on this point too, though.