Humans, like every other organism on the planet, evolved to be adaptable to life on earth specifically.
At this point in our history, we are pretty familiar with the moon (where we've actually sent humans) and other planets and moons in our solar system. There is intense speculation on whether life forms ever existed on those other worlds, or whether life still exists. However, it's patently clear that these planets and moons aren't suitable for human life: unless, perhaps, they were to be radically transformed.
But we don't have the technology to do that yet, and may never.
As for other solar systems: are there other earthlike planets out there in the galaxy and the universe? With billions of galaxies and billions of stars in each galaxy, the laws of probability suggest so. But it's simply not possible to get there. The distance between the solar system and even our closest stellar neighbors within the Milky Way is mind-crushing.
[The farthest unmanned spaceship we've ever sent from the sun, Voyager I, is still well inside the "Oort Cloud" (where comets come from): Voyager 1 is expected to reach the theorized Oort cloud in about 300 years and take about 30,000 years to pass through it.] https://en.wikipedia.org/wiki/Voyager_1
Traveling at speeds we are currently capable of, it would take thousands of years for a spacecraft to reach the nearest star system. Unless we find a way to travel somewhere close to the speed of light, to reach another star system, we'd have to build a spaceship capable of sustaining dozens of generations of people.
Again, we don't have the technology to do that yet, and may never.
tl;dr we must find a way to sustainably inhabit the planet we live on. It's not as exciting as thinking about colonizing other worlds, but it's what we must do. And we know how to. We *do* have the technology. We just have to find the willingness to do it.
Caption this Meme 