Some basics (from someone who played the game a bunch a decade ago): There are two resources, metal and energy, neither can "mine out". To build something, you need equal amounts of both, and the thing building can only spend them at a certain rate ("buildpower"). Notably, metal income is effectively proportional to the amount of territory you control, whereas energy generation can be built anywhere. Buildpower is local to factories and builder units. Neither resource needs to be "moved around", it can be spent by builders anywhere.

One important economy management aspect is matching your metal income with at least as much energy income and buildpower so you can actually spend it (excess energy is turned into a bit of extra metal). And then yes, you should spend it, but the factories support queues (including automatic re-queueing), and you can of course shift-queue buildings.

Another important aspect is that dead units leave behind metal scraps. This can boost your metal income substantially (e.g. if a failed enemy attack leads to a bunch of dead units near your base).

In short, balancing metal income (/territory expansion) with energy income and buildpower is the core economy management loop. But because units have pretty capable AI (e.g. auto-kite when applicable), you can devote a lot more of your attention to this aspect, as well as higher-level decision making.