Volunteering is easy. Grab any device that can record sounds, go on discovery, record lots of wonderful sounds, come back and upload your acoustical discoveries here.
If you like, you can upload your sounds yourself. Or you can ask for help in the forum. Somebody will help you at once. Remember that quality is of no concern.
Perhaps you are fixed to the surroundings of your computer, because your microphone cable is 2m short.
Perhaps you a have a portable mp3-players or mobile phone with recording capabilities. They are mobile and easy. The recording quality that come out of those things is probably the worst, but more importantly it's a good way to start discovering all those surroundings with new eyes - your ears.
You can also plug in a microphone into your mini-disk player or dat-tape-recorder, if you are lucky enough to have such a wonderful setup - record away. Converting the recording into the needed mp3 format is no biggy. If you need help ask.
In any case, at the end we need you to have an mp3-file ready on your harddisk so you can upload it to pdsounds.org with your browser.
At the moment what this project needs most is MORE sounds. Of course there are more way you could help: