A Home theater receiver is basically just a central hub for all your various entertainment devices..
They form the backbone of most entertainment centers. As you might have guessed your receiver outputs sound to speakers, and they are usuall sold seperately and very expensive because of this. Although once in a while you might find a decent HT kit w/receiver and 5.1 speaker setup for around $1000 USD.
Basically a home theater receiver, depending on the model, can have various input sources, and serves as the sole output for any one of those sources. So you only need one connection to the TV - the receiver to the TV.
Receivers can have various inputs for standard RCA Stereo plugs so you can hook up a multidisc player or other device that has stereo RCA outputs.
The receiver usually handles the audio and outputs that directly to its speakers, while passing the video through to the TV via Composite (Single yellow RCA), Component (R/G/B RCA) or HDMI. Some receivers will pass-thru HDMI-audio but not alll.
Depending on brand and price range, it can support numerous input sources, or only one or two. My brother has a rather expensive receiver with many inputs, including 7.1 channel RCA (i.e I could hook up my Sound Blaster X-fi to his receiver, with the Creative Home Theater cable I own.. it takes the standard 3 jacks for the computer on one end, and has tons of RCA plugs on the other, for up to 7.1 sound output) he also has Coaxial (S/PDIF) digital input, as well as fiber optic (TOSLink) input. As well as a mono-RCA jack to send bass to a independently powered subwoofer.
And you usually just select input sources with the remote, or buttons on the unit, just like selecting an input on your TV. So he can watch a DVD, or switch the source to his HD cable box, or to his HDMI PC output to play a game on his TV, etc..
Here is an example of an inexpensive receiver
http://www.newegg.com/Product/Product.aspx?Item=N82E16882120130
and pictures of what the connection options are
http://www.newegg.com/Product/ShowI...YO 5.1-Channel Home Theater Receiver TX-SR307
Here is my brothers receiver. 1050W (150Wx7 channels)
http://www.amazon.com/Pioneer-VSX-1017TXV-K-Satellite-7-Channel-Receiver/dp/B000TDZCOM
The pictures are small but as you can see its LOADED with connections.
(bolded by me)
Pioneer-Exclusive Innovations
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Phase Control (Bass Management System ensures precision low frequency output)
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Sound Retriever for improved Sound Quality of compressed Music Files
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Advanced MCACC Setup with 5-band EQ
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Advanced Direct Energy Power Amplifier
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Front Stage Surround Advance
Features For Superior Sound Quality
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Equal High Power for all Seven channels (150 Watts x 7, 1 kHz, 1.0 % THD, 6 ohms)
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New Freescale 180MiPS Processing DSP
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XM HD Surround Powered by Neural Audio?
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192 kHz/24-bit DAC
Surround Sound Technologies
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THX? Select 2 Certified
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Built-in DTS-ES?/DTS? 96/24/DTS? NEO:6/ Dolby? Digital/ Dolby? Digital EX/ Dolby? Pro Logic IIX Decoders
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WMA9 Pro Decoder
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Advanced Surround (14 Modes, including Front Stage Surround advance)
Enhanced Convenience
* iPod Ready with OSD
* XM Satellite Radio Ready with OSD
* Sirius Satellite Ready with OSD
* Pre-programmed LCD Remote Control Unit
* Digital Video Converter (up to Component)
* Sound Delay
Terminals
* HDMI Video Switching
* 7.1-channel input
* 6 Digital Inputs (2 Coaxial, 4 Optical) and 1 Digital Output
* Component Video Terminal (3 inputs, 1 output)
* Front A/V inputs with Optical Digital Input
* Audio (Tuner included)/Video inputs: 3A/5AV
* Audio/Video outputs: 1A/2AV + 1V
* SR+ Terminal Out
* Large Speaker Terminals (FL/FR/C/SR/SL/SBR/SBL)
Specifications
* Power requirements: AC 120 V/60 Hz
* Power consumption: 490 Watts
* Standby Power Consumption: 0.5 Watts
* Dimensions (W x H x D):16-9/16 x 6-13/16 x 18-15/16 inches (420 x 173 x 465 mm)
* Weight: 33 lbs. (15 kg)