If Alpha Centauri (approx 4.5 light years) is our nearest star, at the highest possible speed for human spacecraft, how long would it take to travel there? People talk about interstellar travel. People do not realize the vastness and distances involved. Inhabiting alien planets or moons would have to therefore reside inside our solar system. Interstellar distances are simply too vast for this possibility.
You are absolutely right about many people not understanding the vastness and distances involved in space travel, especially once leaving our solar system. The New Horizons craft (which visited Pluto) would take about 78,000 years to reach Alpha Centauri. https://earthsky.org/space/alpha-centauri-travel-time. And that was on a craft designed especially small so it could make it to Pluto very quickly, probably faster than speeds a manned ship could reach.
Then there is the problem of once a spacecraft reached Alpha Centauri travelling 36,000 mph, how would it slow down and not just pass it at speeds difficult for humans to comprehend in real world experiences. Here is one illustration that might help. https://www.sciencealert.com/this-gif-shows-how-mind-blowingly-fast-new-horizons-is-travelling-through-space