To keep it as simple as possible, integrated amplifiers have two built in sections, a preamplifier and an amplifier. The preamplifier section will control things such as volume, treble, and base whereas the amplifier section delivers the drive or power to your speakers. These components can be had as individual items giving you greater control over the quality of sound reproduction as well as the ability to upgrade the components. There are many manufactures web sites you can go to and get an idea as to what these components are and what they do, Rotel, Arcam, Outlaw, and NAD to name a few. There are some HT integrated receivers that will give you the option of adding a power amplifier via the preamp out section. Hope this info helps, I know there are some people in the forum that can get into the nuts and bolts of this, maybe you will hear from them as well.
CAV104
