Modal verbs
Hypothetical possibility: would
Would is used to speculate and hypothesise
  about an unreal or improbable present or future situation.
  -   I would
    buy a new car, but I haven't got any money.
 
  -  I wouldn't go on a trip to the moon;  it's
    too dangerous.
 
  -  Tell me, what would you do?
 
In positive sentences would is often contracted
  to 'd in spoken English.
  -   I'd
    come with you, but I'm busy.
 
  - She'd do it for you, you know.