Matrix orientation

Hey all,

What do the components of 3D matrix correspond to? For example,

[x1 x2 x3 tx]
[y1 y2 y3 ty]
[z1 z2 z3 tz]
[w1 w2 w3 1]

I think I get that tx, ty, and tz all relate to the location in 3D space, but where do rotation and scaling come in? And how are the numbers in the fourth line calculated?