Disclaimer: I am extremely new to this and have no proper knowledge of this subject at all, this is just an idea that I had which I want to properly understand. I don't have any knowledge of necessary equations, proper terminology, etc.
In Sci-Fi movies that involve travelling at almost the speed of light, there is sometimes a plot where it involves a character travelling almost at the speed of light for a few minutes or hours, and when they return to earth, they discover that a very long period of time has passed. I know these are Sci-Fi movies, but obviously, this part is not made up.
Now, take this scenario for example. A person aboard some sort of spaceship is travelling close to the speed of light. They travel for a small period of time, maybe a few minutes. For this person, time is moving slower than for a person that is standing still. When this person was to stop, he would find that a long time had passed for everyone else.
Hypothetically, If someone was to look at this person travelling almost at the speed of light, wouldn't they see him travelling much slower than the speed of light? Because if time if passing slower to him, wouldn't he be moving in... slow motion...?
So if it took him a few minutes to travel a very large distance, wouldn't the observer, for whom the time is passing slower, have time to observe the passage of the person moving at the speed of light?
What I don't understand is in this case, it would mean that to the observer, the person is not travelling almost at the speed of light, but much slower. But to the person travelling almost at the speed of light... well, they're travelling almost at the speed of light.
Any help with this is appreciated. If someone can help me, please try to explain the answer in simple terms. If I have gotten one key idea of this wrong, please don't hesitate to correct me.
Edit: I'm not just asking about the time dilation, I'm also asking about the velocity from different POV's.