What do you think the distance coordinates stand for?? I'll bet you just haven't realized yet that what you think you know about spacial coordinates (distances) is incomplete.Try to express it...here or just to yourself. [This stuff IS hard to get your head around at first: That's why it took an "Einstein" to figure it out.]
In non relativistic theory, have you considered a plot of, say, d = vt.....time on one axis, distance on another.....that's where to start....in such a Newtonian setting both time and distance are fixed...that means they appear the same to everybody, they are "invarient"...but that's a low speed illusion...neither is fixed!!!
In special relativity the speed of light is the constant, neither space nor time! SPEED affects different observers measures of space and time in SR. In General Relativty, gravity with curved spacetime, gravitational potential also affects the passage of time and the measure of space.
For a nice introduction to relativity, try here:
which includes :
PS: "If I was at the origin and assigned an event the coordinates (100m,0,0,10s), for example, what does the time coordinate stand for?" It would depend on who measured those values: different observers would provide you different values!!!!
As a next step try reading about "proper time" and "coordinate time"....have fun.