A DVD player is a unit that plays DVDs/VCDs/CDs. It is your source component.
Next in the chain is the amplification of the signal that the DVD player puts out and u can get an INTEGRATED AMPLIFIER or a PRE/POWER OR A STEREO RECEIVER which is basically an integrated amplifier plus a tuner (radio) in the same chassis. This amplified signal is fed to the speakers.
The sequence is source - amplifier - speakers.
The above is for stereo or two channel music.For multichannel music and the home theatre experience u need what is called AVR (AUDIO VIDEO RECEIVER)
Hi In addition to this you can connect multiple sources into AVR like
DVD player's Audio and video to AVR for processing the sound and Video.
STB(set top box like Dish tv,tata sky,Cable STB) audio and video.
PC(Personnel Computer) into AVR
Game consoles like(Play station-3)
This means all sources into AVR and there will be only one output into TV for Video and one Sound output to your Speakers.
AVR Will process the Video/Audio signal from all sources and deliver the output.