Technically an oscilator is a sound creator...
It creates the base sound, like a saw or a sine tone
In yhe pa4x its the part that actually plays the sample..

You can have up to 18 of. These oscialtors in a sound..
A simple stereo sound requires 2 oscilators, one for left and one for right.
Most sounds however are mono..

Now what we do in the synthesis part is actually change the sound of these samples
A filter removes basically the high end or based on type the low end of your sound.
An lfo can be used to add vibration to your sound
Then there is the envelope generator, most important are the attack and the release
Attack is like the fade in of the sound, will it come in fast, or slowly after playing a note
Release iis the sustain after you release the key, will it disapear immediately or very slow..

These are some of the very basics of sound edditing..
All these parameters are on the pa4x basic edditing page

If you want to know more about soundcreation visit keyszone.board.net inhave gathered some articles there about sound creation, they are a good read..

http://keyszone.boards.net/thread/413/subtractive-synthesis-work-beginner

This is a nice one to start with, there are some more articles in that part of the forum.