Units that enter a building cannot leave it the same turn. Every building has its own resources of material and all buildings have a common pool of energy. Some buildings are assumed to have an attached mine and rebuild their material stock slowly. Other buildings have to be equipped with material manually. Material is used to build, equip or repair units.
Energy is used to build, repair or refuel units.
The full list of unit types is attached at the end. Units without fuel cannot move but they still may fight. Refilling is done by either entering a building with sufficient energy or using a dedicated unit like a tanker. Among these are Panzerfaust, MG, rockets, water bombs, bombs etc. Very limited actually.