Since both, space distances, and time intervals, become relative, and the property of simultaneity is lost, we should not separate space and time any more, but talk about space-time.
Sometimes, space-time of SR is also called Minkowski space-time, due to Hermann Minkowski.
In space-time, an object follows a world line.
Depending on how fast objects move, their world lines can be
A major difference between usual flat (called Euclidean) space and Minkowski space-time:
Also, the proper time along the light-like world line (a light ray) is always zero.
Since all physical objects and signals can only move slower than or at the speed of light, all events that can be reached from event A on time-like or light-like world lines form the future light cone of event A. Similarly, all past events from which event A can be reached on time-like or light-like world lines form the the past light cone of event A.
The principle of causality claims that only events within the past light cone of event A could have influenced event A: looking at a distant star is equivalent to looking backwards in time. If we look at the Sun (never do it without dark glasses!) we see it as it was 8.3 minutes ago.