It's a very simple and easy to understand system
Money or things gained from trading or selling items/products are converted into system points at a 1:1 conversion rate.
With system points our MC can buy modded items/units/blueprints.
A simple example would be, our MC traded the FellBlade for 700000 Skaven slaves, the system would go "hey! those Skaven slaves are worth 0.25 system points per entity you can trade it or not".