F15h,
I'll take a stab at explaining preamps, int. amps, and receivers.
A preamp(lifier) basically a separate box that takes the signal from all of your devices e.g. a cd player and an FM tuner and routes it to the power amp(lifier) which amplifies the signal and sends it to the speakers for you to hear. It also provides volume control. Think of the preamp as a switchbox with volume control. Some preamps really are that simple. Some preamps are much more complicated: providing Digital-to-Analog Conversion (DAC), video routing for Home Theater, built-in FM/AM radio tuners, etc. But the result is essentially the same, you select which device you want to listen to and the signal is routed to the power amplifier.
An int(egrated) amp combines the functions of the preamp and the power amp in a single box. Usually these are limited to 2-channel i.e. stereo signals and generally do not handle video. And I think that most int amps do not have DACs or tuners. Of course there are always exceptions.
A receiver also combines the functions of the preamp and the power amp. But it usually also handles video signals e.g. from a DVD player or VCR. And most receivers these days are multi-channel, usually 5 - 7 channels, because of the popularity of Dolby Digital and DTS. And receivers also generally have an FM/AM tuner built in.
These are oversimplifications. But I didn't want to overload you with too much information.