The term "Spacetime" has an almost mystical connotation. But it seems a lot more complicated than it is.
The basic premise of putting the two concepts together, space and time, is there's no such thing as stillness.
Imagine any day. We wake up, we go do some things, we go back to bed. The next day, we say we wake up again in the same place.
In common sense, everyday usage, "the same place" is correct. Zoom out to a larger scale, and it's not.
The earth rotates completely in 24 hours, so it faces the same position towards the sun. But it also orbits the sun; so in a day, it has moved 1/365th of that distance. If you could drop an cosmic anchor out your window one morning, absolutely stationary, it would be tens of thousands of miles away the next day.
After a year, the earth has moved 365/365ths around the sun. Like each morning, it's in the same relative position to the sun as a year before. But you won't come back to the anchor. The sun also orbits around the center of our galaxy. The absolute position – the anchor – is hundreds of thousands of miles away a year later. The galaxies move too, so a 300 million galactic year doesn't come back to the "same" place either.
I sit here typing, watching the clock on my wall. We say we sit still and watch time go by. But me, and you, and the chair and the clock are all racing through space.
Say you ran down the street with a clock strapped on your back. After sixty seconds, the hand would have made a full turn.
Someone running directly behind you would say the hand is now back where it started. But if there was a smoke trail off the second hand, someone sitting on the sidewalk would have seen it trace a spiral in mid-air. From the point of view of the anchor, instead of moving in a circle, clock hands actually move in a spiral.
Time is motion, and nothing ever stands still.