It’s hard enough keeping up with the different locations, characters and events that take place across Marvel’s Cinematic Universe. But throw in the Infinity Stones, and things can get downright confusing.

Since Iron Man hit the big screen back in 2008, Marvel has slowly been building toward a larger shared universe, one that will ultimately culminate in Thanos possessing the Infinity Gauntlet. With Phase 3 finally here, now’s as good a time as any to refresh your memory as to what the Infinity Stones actually are.

Perhaps Benicio del Toro’s flamboyant Collector summed it up best.

“There were six singularities. Then the Universe exploded into existence and the remnants of these systems were forged into concentrated ingots: Infinity Stones.”

It’s these stones that Thanos is trying to collect in his quest to control the universe. Their importance to the MCU can’t be understated; heck, the next two Avengers films have “Infinity War” in the title. We’ve actually already seen a teaser of Thanos brandishing the Infinity Gauntlet with a menacing smirk, so it will be the Avengers’ job to wrest control from the ultimate super villain.

We still haven’t seen all the gems yet—we’re waiting to check out the Soul Stone and Time Stone—but you can bet they’ll be introduced as Phase 3 kicks off with next year’s Captain America: Civil War.

If you’re unsure about what the Infinity Stones are and where they ended up, the video above is a nice guide to get you up to speed.