A strictly three-dimensional world is pretty boring. Nothing happens in it. Suppose you tell your friend that you will meet her at the entrance to the Washington Monument. Your well intentioned instructions will help her narrow your location in the universe to a six foot cube of space at a particular point on the surface of the earth. But unless you also say when to be there, the instructions are useless.
Time is a vital fourth coordinate or dimension to our world.
Now, much like the frozen images captured on a photograph. Space and Time taken together define the complete arena in which we live. They form such an integral, cohesive framework for our existence that physicists since Albert Einstein refer to their combination as simply 'spacetime'. Spacetime is vast. It extends well beyond the earth and solar system, encompassing the entire universe out to the farthest galaxy.