Thanos is trying to collect and control all six Infinity Stones to power the Infinity Gauntlet.
Each time the Infinity Stone Die is rolled for a turn, note the color rolled and add a counter to the matching Infinity Stone Card.
At the end of each turn, any Infinity Stone Card with five (or more) counters has been collected by Thanos. This is denoted by placing the Stone into the Infinity Gauntlet and flipping over the card (removing all the counters). This now grants Thanos extra abilities that will activate on every subsequent turn when that color is rolled on the Infinity Stone Die – instead of adding counters!
Infinity Stone abilities DO NOT trigger on the turn the Stone is collected.