The slide Slides are usually made of glass or metal . The easiest and un-coolest way is to go into your guitar shop and buy one. The coolest way, but hard to play is using a bottle. You have the choice between middle finger, ring finger and the pinky. The index finger does not work, because you need a least one finger to mute the other side of the strings.
All fingers have advantages and disadvantages.
The middle finger. The ring finger. Duane played this way. The slide is big enough to get a good sound and you have two fingers left for muting the strings. But playing the normal way is hard.