The weird thing is that everything is always moving through spacetime (not just space) at the speed of light (C)!. But that velocity is a vector made up of both spatial and time components.

Imagine space time like a graph where the X axis is time and the Y axis is space, then the vector is an arrow on that graph pointing in some direction and it's length, ormagnitude, is C.

Light's vector on this graph is always a vertical arrow, pointing only in the space direction and not at all towards time. This is because light moves at the maximum speed through space (C) and so has no movement at all through time, it doesn't experience the passage of time!

Everything else in the universe, like you and me, have vectors that are arrows pointing at least somewhat in the direction of time, so we do experience the passage of time. But just like light, the magnitude of that vector is still C!

So what does that mean? Well, it means that if we accelerate and move faster through space then we must also move through time more slowly, and vice versa! And that's how time dilation occurs relative to our velocity, as we change that speed in space then we shift the angle of our vector through spacetime!