What Audio Ports Do You Have?
Computer:
Most notebook computers will have two ports for audio:
1. Headphone (output);
2. Microphone: (input).
Use the output for connecting the audio portion of your presentation to speakers or amp/mixer.
The type of connector you need is most probably an 1/8 inch audio plug (plug, more precisely "telephone plug," is terminology that began with this type of cable end being used when telephone operators connected phone calls by hand by quickly plugging and unplugging the telephone lines in the early switchboards).
"Telephone plugs" come in at least three sizes. You will work with two of these: 1/4"
and 1/8".
Connect with your computer audio output using an 1/8 inch 
plug-ended audio cable, inserting it into the "Headphone" port.
The other end of the cable may have an end that can be plugged directly into the projector, speaker or mixer/amp; however, if it doesn't DO NOT WORRY. There are adapters available that came with your equipment (or can be purchased at Radio Shack and similar outlets). More on this in "Connecting to the Mixer/Amp."
VCR: The back of a VCR player or recorder/player will have composite audio connections.
Higher-priced vcrs, such as the one in the picture at the left, will have two audio outputs (color-coded red and white; one of these for each of two channel "stereo"). Lower-priced vcrs will have only one audio output port (often white in color). The yellow port is for Video.
CD: The CD Deck will have the same audio outputs as the VCR.
DVD: The DVD deck will have the same audio outputs as the VCR.
Camera: Consumer level cameras will have either a composite audio output or a plug connection at the end that connects to the camera with three composite-type plugs at the other end. (Audio connections are red and white; video is yellow).
Professional level cameras will have multiple audio outputs. The best will be the balanced outputs (XLR male at right) more commonly seen on microphone cables and mixer/amp boards.