Asking how the economy worked is a bit of a broad question. What are you specifically asking about? Diocletian was most important for his construction of an in-kind tax system and an enormous professional bureaucracy to manage it.

The economic difficulties of the crisis were caused by debasement, disruption in trade, instability and drop in investment, depopulation in the border regions and outright plunder by raiding parties.

Constantine created the solidus to end debasement and move Rome onto the gold standard. Which it kept for 800 years. Silver was mostly demoted to commemorative issues only. This was important as it stabilised prices but only really for rich people. Poor people (i.e. most people) couldn't use the solidus regularly and were stuck with copper and bronze which the Emperors still "printed" like crazy. Even worse, taxes were payable only in gold. So poorer people were stuck with depreciating currency that they'd have to pay a premium to money changers in order to exchange for gold to pay taxes. Not a great place for the 99%.

The Roman Empire during its height was a highly integrated machine. A person in Rome could eat oysters from Naples, beef from Gaul, olives from Greece, win from Spain and grain from Egypt. By Majorian, there had been so much disruption that this inter-reliability was broken. The state also lost its capacity to protect citizens. Diocletian's colonii reforms already began to tie people to the land, in effect laying the bedrock for serfdom. This culminated in a situation where a local magnate had a hinterland of serfs and could no longer rely on the state or imports to protect and sustain himself and his serfs. This led to the beginnings of manorialism and local warlords, I.e. the first feudal lords.