I dont have the modern DLC's , but usually there is support supply units on map edge. At times they are frozen until a set turn. When there free they have to be next to the units needing supply, either moving them to the unit or the other way around.I believe resupply is automatic, within limits.
The game has a high learning curve but it's worth it and there are some great gaming moments to be had. There are alot of threads here with alot of the same questions you will have like we all did at the beginning and still do with each update because frankly the documentation and explainations have sucked Click the box at the top of the thread to show all topics instead of 365 days and read some threads, i guarantee you will pick up some useful info.
Enjoy when you can, and endure when you must. ~Johann Wolfgang von Goethe
"Be Yourself; Everyone else is already taken" ~Oscar Wilde
*I'm in the Wargamer middle ground*
I don't buy all the wargames I want, I just buy more than I need.