How to play a B7 guitar chord is clearly explained in the following video guitar lesson:
A B7 chord, also known as a B dominant 7th chord or Bdom7, contains four different notes that give it a characteristic sound. The root note is of course a B, the major 3rd is a D# note, the perfect 5th is an F# note and the dominant 7th is an A note.
The first thing in this video lesson you learn is the best shape for this chord on your guitar, which is an open position B7 guitar chord:
Here is the B7 chord guitar TAB:
This chord shape should be fairly comfortable for you to hold, even though you are required to use all four fingers and need to make sure the open B string rings clear. The best piece of advice for holding most guitar chords is that you always need to keep your fingers curved unless the particular finger is doing a bar. Only the fingertips should be touching the fretted string, and enough room needs to be made so open strings can also ring clearly and not be accidentally muted by a fretting finger!
The second part of this chord lesson shows you a challenging B7 barre chord shape beginning at the 7th fret position on the E string. Note that this chord can also incorporate a high dominant 7th note (in this can an A note), which really brings out the bluesy quality of the B7 guitar chord.