Big question. I'll start you off--
(1) 'Would' is a more polite, hesitant, or circumspect form of 'will':
'Will you paint my Porsche?' vs. 'would you paint my Porsche?'
'I will be happy to help you' vs. 'I would be happy to help you'.
'I will visit you when I come to town' vs. 'I would visit you if I came to town'.