The "b" means to bend the note for example "7b" (bend the note on the 7th fret upwards)

The "h" means a hammer on from one note to the other like "7h9" (strike the note on the 7th fret and without striking the note again put your finger on the 9th fret.)

The "p" means a pull off from one note to the other for example "9p7" (after striking the 9th fret without striking the string again, pull off to the 7th fret).

The "x" is a muted note. (just means to mute a string, place your right hand over the strings, bearly touching the strings, then pick the muted string)

I can't really explain it that great, but maybe there is someone else out there who can explain it better. Hope it helps a little bit.