With the six Infinity Stones, he’ll be able to do that across all of reality with a snap of his fingers.
In the MCU, when Titan started running out of resources, Thanos suggested that half the planet’s population be exterminated to save the rest.
Unlike in the comics, where Thanos is obsessed with courting the personification of Death, Thanos’ reasons for collecting the Infinity Stones in Avengers: Infinity War stems from him not wanting the rest of the universe to fall prey to the same fate his homeworld, Titan, suffered.
As a result, Thanos has been traveling across the universe and eliminating half the population of each planet he visits as his way of course correcting.