Requests are used when you want someone to do something for you.  The modals can, could, will and would are used as in the following examples.  There is no difference between them, which means that you can use any of these words and it’s the same.  Please can be added to make your request more polite but is not necessary.

Can you, Can I:

Can you tell me when the store closes?
Can you please help me find my dog?

Can I borrow $20, please?
Can I see some identification, please?

Could you, Could I:

Could you give me your email address?
Could you tell me the time, please?

Could I get a ride home, please?
Could I meet with you tomorrow afternoon?

Will you:

Will you give me a ride downtown, please?
Will you please pass me the salt?

Would you:

Would you please stop making all that noise?
Would you sit down here next to me?

(Notice that the verb after all these modals is in the simple form.)

Here are other ways you can make a request:

Would you mind:

Would you mind closing the door on your way out?
Would you mind turning down the music a little?
(Notice that the verb after would you mind is a gerund (-ing))

I would like:

I would like you to join me for dinner.
I would like another cup of tea, please.
NOT:  I want another cup of tea, please. (This is a little impolite)

I’d (really) appreciate it if you can / could / will / would.

Really is optional.

I’d really appreciate it if you can lend me a little money until payday.
I’d appreciate it if you could let me use your car this Friday.
I’d really appreciate it if you will wait for me.
I would appreciate it if you wouldn’t text me all the time.

You can also drop the modal, but you must put the following verb in the simple past tense.

I’d appreciate it if you dropped me off downtown.
I would appreciate it if you waited for me outside.