Dear Dr.Guitar,
Once again I am in need of your expertise in my quest for guitar-playing greatness.
I am presently studying the "TAB" system of musical abbreviations and symbols and find myself in a bit of a pickle!
I have a comprehensive guide to the many symbols contained in the "TAB" system but am regularly confused by the explanations therein. For example;

H.= Hammer on. No guidelines as to which part of the instrument hammer on or with what grade of hammer?

BD.=Bend downwards. I find this a most uncomfortable position to play in and would like some advice with regard to wether I should be bending from the knee or back.

LD.=Let down. Pretty much how I feel after purchasing my TAB guide!

PO.=Pull off. Is this some sort of post-gig activity?

X.=Dampened string. Surely not a safe combination with electricity?

I hope that, as in the past, you can shed some much needed light on my dilemma and restore my faith in the guitar playing community.