What the "d" here stands for?
for example: you'd.....; they'd.....; he'd.....

Question

Answer

The 'd is a short form of "would" or "had".

Answer

Yes, it's either "would" or "had".  You'll know which one it is based on the following verb.  "Would" is always followed by the verb in the base form, and "had" (ie. past perfect "had") is always followed by the past participle.

You'd ask = you would ask
You'd asked = you had asked

Answer

would or had

Answer

you would,they would,he would.
or
you had , they had,he had

depends on the sentence

http://www.thefreedictionary.com/he%27d

Answer

Is the contraction of: 
You would....They would....he would