Difference between Can and Could

It sound really simple but yet its a little confusing while we use this to words. 

Can and Could

This is the most common error, we usually make and get confused with while using it.

Lets understand it with some examples and use

Uses in REQUEST

Telling or asking someone to do something.

Can is less polite

(mostly used in Informal way)

- Can you open this jar

and

Could is Very polite 

- Could you open this jar.

.

.

Uses in ABILITY

Can is used to describe present ability

- I can dance

and

Could is used to describe past ability 

- I could dance when I was younger

.

.

Uses in PERMISSION

Can is used to give or take informal permission

- Can I use your pen

and

Could is used to give or take formal permission 

- could i use your pen

.

.

Uses in POSSIBILITY

Can is used to describe present possibility

- They can come by train

and

Could is used to describe past possibility

- They could come by train

Looking at the examples i hope you understand the difference between

CAN & COULD so now you can use it in your own sentences without any confusion.