The easiest way to play slide guitar is to first adjust your guitar to an open tuning - in this particular lesson we're going to use Open D Major tuning for our example.
Be sure to checkout my course Essentials of Slide Guitar - this short lesson is only scratching the surface of what I covered in there!
The reason I've chosen to use an open tuning is because a slide isn't like your fingers; you can't bend it into a new shape for every chord you change to. As a result, it is easier to adapt the tuning of our strings so that they work well in a straight line. In other words, we're going to tune the guitar so that when we strum all six strings without any fingers on the frets, it will create a great sounding D major chord.
Then, we can simply add the slide at any point on the fretboard and create another major chord.
D Major tuning is simply D A D F# A D.
awsome now i can play like derek trucks what a slide god reminds me of ONE OF THE GREATEST DUANE ALLMAN