So in this mod, there is no "supplies" as you know them in reforger. Resources are turned into materials which are turned into objects at the factory or the field and shipped to bases.
Basic resources can be used to build field constructions to make AT, Rifle, or MG AI defenses. Weapons and ammo need to come from a factory. The supply/need for supplies is a key feature of attritional warfare - choking off your enemies supplies and forcing them to capitulate/fight at very reduced power.
Generally a base is loaded with ammo/supplies. You can think of bases/spawns, as an arsenal but with amount limits vs supply costs. Normally a well supplied base would have like 300 guns, 500 ammo, 150 grenades - very limited risk of running out of general weaponry unless not supplied for half a day or so, or if it suddenly gets in a massive fight for its life.
Running out of "stuff" is generally only a problem in a huge fight, thats when supply trucks and logi become critical - flooding the base with resources to keep up with the constant respawn/death/losses. Thus keeping the supply lines open, and the factories cooking, the resources mined, becomes evermore important.