Space aliens and other civilizations almost surely exist. However the universe is so vast that we may never be in contact with them. Our galaxy, The Milky Way, has at least 200 billion stars. About 7% are stars like our sun, and and half of those may have habitable planets. These are just the planets that could support our kind of life. There may well be other forms of life too.
NASA says there are several hundred billion galaxies. So, yeah, space aliens and life others certainly exist. The universe is probably teeming with them.
However, the nearest star to our sun is Proxima Centauri. It’s 4.35 light years away. Even if we somehow determined there was intelligent life to contact or habitable planets to live on there, it is not possible to travel there.
The fastest outward-bound spacecraft yet sent, Voyager 1, has covered 1/600 of a light-year in 30 years and is currently moving at 1/18,000 the speed of light. At this rate, a journey to Proxima Centauri would take 80,000 years
Also, any space ship traveling to other stars would need to produce food, provide clean water, have ample fuel, be able to do needed repairs and maintenance, and be gone for centuries. Forget Star Trek. That’s not doable using any technology we have or even fantasize about having.
Also, um, how would the space ship get back to earth? It’s not like it could use a GPS.
Even a super-advanced civilization that had survived for a billion years would not be able to travel at anything close to the speed of light. Thus, it would expand in its area only. And not go exploring elsewhere for centuries, as there would be little reason to do so.
Also, let’s say earth analyzed a strange new signal from another galaxy, and determined it it could have only been sent by an advanced civilization as a beacon. Except it’s from a million light years away. Pretty sure we won’t be having tea with them any time soon.