The word would has a few meanings and cases of use in English. Grammatically, "would" is the past form of "will". We do not put "to" before the main verb after "would" and the main verb stays in its infinitive form.
We often shorten "would" to 'd (I'd, you'd, we'd etc.). Do not confuse the shortened versions of "would" and "had".
1. I would help you, but... — conditionals
Would is used in conditional sentences.
When we imagine or think of something which is not real, we use would + infinitive.
When we express regrets about something in the past, we wanted things to go otherwise, but we can't change that anymore, we use would + have + past participle.
I would go to the cinema tonight, but I don't have anyone to go with. (but I still can go if I find a company)
I would have gone to the cinema yesterday, but I didn't have anyone to go with. (I regret it but I can't change it)
John would come to the party tomorrow, but he won't have time. (but he still can come if he has time)
John would have come to the party last week, but he didn't have time. (he regrets it but he can't change the past)
Diane would buy a new car, but she doesn't have enough money. (she can still buy it if she has money)
Diane would have bought a new car last month, but she had to spend all her money on home renovation. (that happened last month so she can't change that)
2. She said she would come — reported speech
We use "would" as the past of "will" when we need to harmonize tenses in two parts of the sentence, for example, in the reported speech.
Anne says she will come → Anne said she would come
I promise I will write → He promised he would write
They are sure they will be on time → They were sure they would be on time
3. He wouldn't listen — refuse
We use "won't" and its past form "wouldn't" in the meaning of "not want", "refuse", "be unwilling" to do something.
I'm trying to talk to him, but he won't listen. (= he doesn't want to listen)
I was trying to talk to him, but he wouldn't listen. (= he didn't want to listen)
— Why are you angry? — The car won't start. (= it "refuses" to start)
He was angry because his car wouldn't start. (= it "refused" to start)
4. Would, used to — habits in the past
We use would as an analogue of used to when we speak about some regular actions and habits in the past.
When I was younger, I would drink five cups of coffee a day. (= I used to drink...)
Do you remember? When we were kids, we would run through the field, climb the hill and hide under the big oak tree. (= we used to run...)
In the examples above, we can either say "would" or "used to". But we can only say "used to" when we talk about states in the past and not physical actions.
When Fred was a student, he used to have a beard. WRONG ... would have a beard, because it isn't a regular action
When we were children, we used to live in the countryside. WRONG ... would live, because it isn't a regular action
5. Would you please, I would like, would you mind — polite request and set phrases
We use would to make a polite request. It is also possible to use could (could you please...?) in the same manner.
Would you please help me?
Would you close the window, please?
Would you carry this bag, please?
Would is part of some polite set phrases, like:
- I would like, would you like
- I would rather (do something)
- Would you mind (doing something)