CAN AND COULD
In this article, we tell you about the word "can" in English. It has three different meanings and here they are.
One meaning of can is "ability" or to be able to do things.
I can drive a car.
She can cook.
They can speak English.
Another meaning for a can is "permission". When you want to be allowed to do something you use "can".
Can I park here officer?
Can I go out for a minute?
Can I take a day off tomorrow?
The next meaning for can is "request". When you want to ask for something then use can in your request sentence.
Can you give me a glass of water?
Can you give me a ride?
Can I take my shoes off?
As you know "could" is the past tense of "can". But only if the meaning of can is "ability".
I can drive.
(past tense) I could drive until last year but this year I can't because an officer took my license.
I couldn't call you yesterday because I was busy.
She couldn't come to my party because she had a guest herself.
But if "could" is not the past tense of "can" then it has the same meaning as "can".
Meaning of "request".
Could you please give me a cup of coffee?
Could you please help me with these boxes?
Could I tell you the news later?
Meaning for "permission"
Could I sit here?
Could I go out for a minute?
Could I put my chair next to you?
So to summarize we should say that can and could have three different meanings but could is more polite and formal when used as a request or permission.
Hope the article has clarified the confusion that some English learner have.