Mostly, he played slide guitar using a pocket knife and then a slide made from a beef rib bone, later switching to a glass slide. He played with the slide on his ring finger.
In the 1950s, people became more interested in Blues Music and McDowell became more famous. He recorded for the first time in 1959 with Alan Lomax and Shirley Collins. He started playing on electric guitar rather than acoustic but said "I do not play no rock and roll". He taught Bonnie Raitt the slide guitar technique, and was written about by The Rolling Stones'.
McDowell's first album came out in 1969, called I Do Not Play No Rock 'N' Roll.
Fred McDowell Facts for Kids. Kiddle Encyclopedia.