Though often used as an additional tool in a guitarists arsenal, most folks don't know that playing with a slide was actually born out of necessity. Back in the 1920's Tennessee, a man named Cletus Earnest Henry McCracken was playing around with his guitar while maintaining his daily ritual of draining as many bottles of wine as he could muster. Sure enough, about halfway through the day he wound up getting his left ring finger stuck inside the mouth of a wine bottle. After, he and his drinking buddies tried desperately to pull it off to no avail, he figured he'd just break the bottle. So he whacked the bottle on the rail of the nearby train tracks and it broke. Well, most of it broke. He looked down to find that the neck of the wine bottle was still stuck on his dang finger! "Aw, to hell with it," he said. "Let's keep pickin." And with that he picked up his guitar and commenced to sliding his bottlenecked finger up and down the strings and, wouldn't you know it, it produced a not altogether unpleasant sound. Cletus' eyebrows arched upwards! "I reckon I like this here sound!" As he continued to slide his finger along the strings he exclaimed "By golly, I've invented a new kind of playing! I think I'll call it 'broken-bottle-stuck-on-yer-finger style!'" Before long, word spread of Cletus' 'broken-bottle-stuck-on-yer-finger' style and soon people just took to calling it slide.
Now you can follow in Cletus' footsteps, but it's much easier to just go to your local shop and buy a pre-made glass or brass slide. So go on and get yer' slide on!
Disclaimer - This story may not be true