i knwo this sounds stupid but ive never understod what a slide does......laugh at me but im just slide retarded
It's kinda just like when you do regular slides on the fretboard, the difference is that the transition between notes isn't every half a note. It gradually changes. Also the vibration between the strings and the slide alter the sound a bit. You can go off the fretboard and around the pickups for even higher pitched noted. That just about sums it up.
The only way to find out is to find some videos or songs of people who used slides. Search 'slide guitar' into video.google.com or something like that and see what comes up.