Speakers are not a powered item. They do not plug into the wall or generate almost any volume at all. You need amplification to get any appreciable volume out of speakers.
To do this, you could just get a stand alone amplifer, but those generally have small knobs on the back to adjust the volume level and you typically only run stereo audio into the back of the amplifier. So, you get good stereo amplification for your speakers, but lousy volume control, no surround, no digital connectivity, no way to connect multiple sources, no video connections, and no remote for the volume control.
The A/V receiver combines it all. You get the ability to connect video sources like a cable box, VCR, and DVD player into one device. There is an amplifier built into the A/V receiver that will give you solid audio output to connect your speakers to. You get switching capabilities so you can connect multiple devices (DVD player, cable box, etc.). Finally, you get the remote control which allows for volume control, switching of sources, and other adjustments or features that the receiver may have. Many receivers have FM tuners built in so you get radio stations on them. Some are now shipping with XM Radio built in. Many are SURROUND receivers so you can setup a 5.1 to 7.1 audio system with multiple speakers.
So, it sounds like you gotta go through some more of the basics to get up to speed on what is what. Google some of the terms you may not be familiar with. Go ahead and ask if more questions come up.
I don't recommend DVD player/receiver combo units, but suggest you get a separate receiver and DVD player. This way you can upgrade each component as money allows for it. Some very good deals can be had on used gear via eBay if you are careful and shop around a bit. I know my old entry level Kenwood setup which was several hundred bucks at Sams Club probably would sell for only $50 or so on eBay - yet would make some people very happy for that price. So, do some homework and read some reviews and figure your terms out.
