The modal WOULD to express unreal situations

Present and future

Would + infinitive can refer to unreal situations in the present or future. An unreal situation is one which is not true in the present or one which may or may not happen in the future:

It would be nice to live by the sea. (I don't live by the sea)
It would be great to go hiking in the Appalachians again. (I may or may not go)

Would is often used in the main clause of a sentence in the second conditional:

I wouldn't do that if I were you. (I am not you)
I would help you if you asked me to. (you may or may not ask me)

Past

Would + perfect infinitive refers to unreal situations in the past. We imagine a hypothetical past situation which did not happen. We often use an if-clause to describe the situation:

It would have been wonderful to meet you in person.
I would have helped you if you had asked me to. (you didn't ask me)