A great place to start s the instructional video my friend Lee Roy parnell did a few years ago called "The Art of
Slide Guitar."
Lee Roy doesn't come across as arrogant or coneescending in any way, the music he makes with the band he had at the time (some of whom are also my friends) is great and you'll come away knowing a lot more than you did before. It's truly a great place to get started.