Kenil Rajyaguru

So how the time travel (dilate or one can say time difference or relative works) ?

I don't understand the concept of when we move in light speed we age less than in earth. Why? Is it coz of the gravity. Internet says that when gravity increase, the time becomes slows. So in the space one must age faster than the earth. But it isn't like that. One more thing when we move with light speed, gravity will be generated inside the space shuttle, but it won't be more than the earth. Again they say when gravity increase, time slows..so moving with light year we should age more 🤔 If going through my theory, earth may had less gravity in past time and eventually increased with the time, due to that reason life span of human decreased with time and also the height.