Probably it's a good idea to understand rotations in two dimensions first. If you fix the origin, a rotation is just a transformation that preserves lengths of line segments. If the angle is theta, then the transformation from the old coordinate system (x,y) and the new system (x', y') is given by
x'= cos(theta) x -sin(theta) y
y'=sin(theta) x + cos(theta) y.
Now, in special relativity, if a point in space time has coordinates (t,x), what is preserved is c^2 t^2 -x^2 (rather than lengths of line segments). When this is done, the new coordinate system (t',x') turns out to represent the perspective of an observer that is moving relative to the original. When written in terms of velocity, the transformations are a bit complicated, but they can be reduced to
ct'=cosh(eta) ct -sinh(eta) x
x'=-sinh(eta) ct +cosh(eta) x
where hyperbolic trig functions are used rather than the usual ones.
If you take this perspective, many paradoxes of relativity become easier to understand. For example, the lengths x and x' of an object won't be the same for the two observers just as the x coordinates wouldn't be the same after a rotation.