Thanos's quest for the Infinity Stones was a decade-long, unwavering mission to "balance" the universe by wiping out half of all life. His strategy involved identifying the location of each stone and using overwhelming force or manipulation to acquire them. He did not collect them in the order they were introduced in the MCU, but rather in a specific sequence that culminated in the Snap. Here's how he acquired each one:
Thanos's first confirmed acquisition in Avengers: Infinity War was the Power Stone. He attacked Xandar, the home planet of the Nova Corps, who were safeguarding the Orb containing the stone. He decimated the Nova Corps and the planet's population, extracting the stone from the Orb and placing it into his Infinity Gauntlet.
After Xandar, Thanos intercepted the Asgardian refugee ship carrying the survivors of Ragnarok, including Thor, Loki, and Hulk. The Space Stone, previously housed within the Tesseract, was in Loki's possession. Thanos tortured Thor to force Loki to reveal its location. Loki, in a desperate attempt to save his brother, handed over the Tesseract, which Thanos then crushed to reveal the Space Stone. He then killed Loki.
Thanos traveled to Knowhere, the celestial mining colony, where the Collector was supposedly keeping the Reality Stone (Aether). He used the Space Stone to teleport to Knowhere and confronted the Collector. While initially appearing to be a struggle, it was revealed that Thanos had already acquired the stone and was using its power to create an illusion to trick the Guardians of the Galaxy. He transformed Drax into blocks and Mantis into ribbons, demonstrating the stone's power, before leaving with it.
The Soul Stone's location was a mystery, guarded by the Red Skull on the desolate planet Vormir. To acquire it, Thanos had to sacrifice someone he loved. He brought his adopted daughter, Gamora, to Vormir, knowing she was the only one he truly loved. Despite Gamora's pleas and resistance, Thanos threw her off the cliff, sacrificing her life to obtain the Soul Stone. This was a pivotal and emotionally devastating moment for him.
Thanos then traveled to his ruined home planet, Titan, where he confronted Iron Man, Doctor Strange, Spider-Man, and the Guardians of the Galaxy. Doctor Strange, the Sorcerer Supreme, wielded the Time Stone within the Eye of Agamotto. After a fierce battle, Strange, seeing millions of possible futures, realized there was only one path to victory. He willingly surrendered the Time Stone to Thanos in exchange for Tony Stark's life, knowing this was part of the one future where they eventually won.
The final stone, the Mind Stone, was embedded in Vision's forehead. Thanos's forces invaded Wakanda to retrieve it. During the battle, Wanda Maximoff (Scarlet Witch) attempted to destroy the stone, killing Vision in the process, to prevent Thanos from getting it. However, Thanos used the Time Stone to reverse time, resurrecting Vision only to rip the Mind Stone from his head, killing him again. With all six stones in his gauntlet, Thanos then performed the Snap.
Pro tip: The Infinity Gauntlet itself was not an Infinity Stone, but a powerful artifact designed to channel and contain the immense power of all six stones, allowing Thanos to wield them simultaneously. Without the Gauntlet, he would not have been able to survive the combined energy of the stones.