Phrygian Dominant Scale
The phrygian dominant is a tricky scale, and requires a bit of finger stretching to play properly. Start with your first finger on the root of the 6th string, and play each note in the scale slowly and evenly. Your first finger should play both the first and second notes on the fifth string (stretch your finger down one fret to play the first note on the string, then slide it back to "home" position to play the second note.) Play the phrygian dominant scale accurately, forwards and backwards. The two bracketed notes on the first string indicate usable scale notes that go beyond the two-octave scale pattern. Play the notes on the last string using your first, second, and fourth (pinky) fingers (the last note will require a pinky stretch).
Using the Phrygian Dominant Scale:
The above graphic illustrates the diatonic chords for the D phrygian dominant scale. Playing through these chords will probably be less than inspirational for songwriting purposes - the phrygian dominant scale doesn't provide a set of chords nearly as nice and tidy as the major scale. Songwriters generally stick to writing songs that only include the root major chord (and sometimes also using the bII major chord). Experimentation is the key here. Try putting your guitar into open D tuning (DADF#AD) and playing up the phrygian dominant scale on the first string, while strumming all six strings. Now, try to create a riff using the scale. Try it a few times, and you'll get the hang of it.
The phrygian dominant scale is actually a mode - the fifth mode of the Harmonic Minor scale. So, the D phrygian dominant scale actually has the same notes as a G harmonic minor scale. For further information on the modes of the harmonic minor scale for guitar, visit this web site.
When used for soloing purposes (in a pop/rock context), the Phrygian Dominant scale also usually works best in situations where a chord progression lingers on a single major chord for a long period of time. It is a very distinct and strong sounding scale, so it will sound very out of place in many situations.
In a jazz context, the phrygian dominant scale gets used in a much different situation; generally on a V7 chord, to create an "altered dominant" sound. For example, on the chord progression G7 to Cmaj, the G phrygian dominant scale would be played on the G7 chord, to create a G7b9 sound, which resolves nicely to the Cmaj. The phrygian dominant scale is also used on V7 chords in minor keys (G7 to Cmin).
Practicing, experimentation, and jamming the Phrygian Dominant scale will eventually yield some very interesting and exciting results for the experimental guitarist. Best of luck!