I have been unable to find a clear explanation to this basic question which is at the core of my lack of understanding the relativity. Everything I've found is either too general, or too technical. Please excuse my simplifications and lack of technical language. As I understand it (in very simple terms), given two objects, the one which is moving faster relative to the other will experience time going by at a slower pace. What I don't understand is, given two objects in space, how can one be said to be moving faster or slower RELATIVE to the other? Wouldn't they both be moving at equal and opposite velocities RELATIVE to one another? I don't understand. Can someone please shed some light, or direct me towards some reference material to help me with this? Thank you in advance.