Intergrated or Solid State Whats The Difference ?

New to this equipment and I do not understand (quite a few things)the difference between an Intergated and a solid state amp, or the Pros and Cons of each.
And another thing, how do mono blocks provide enough power to drive power hungery speakers like VSA VR4's or B&W 800 or 802's. Seems to me the average tube amp provide 50 to 80 wpc.
Thanks