To play the E note, pick the open 6th string.
Play the F note with the first finger of your left hand behind the first fret of the 6th string.
Play the G note with the third finger of your left hand behind the third fret of the 6th string.
The Dobro is a metal bodied "Resonator Guitar". It has a resonator cone which amplifies the sound even though there are no electronics involved. There are also wooden bodied guitars with a metal resonator cone. All these guitars are great for slide and fingerpicking. They are traditionally associated with Blues, Bluegrass, Country and other Roots music.