You use CAN to describe an ability in the present.

Annie can swim, but she can �t ride a bike.

You can also use BE ABLE TO to describe an ability in the present or future.

(Attention : CAN is used much more frequently than BE ABLE TO in the present tense)

He �s able to park a car, but he �s not able to drive in traffic yet.

I �ll be able to speak French in a couple of months.You use either COULD or WAS/WERE ABLE TO to describe a general ability in the past

I could swim when I was 5 years old.

My brother was able to drive cars when he was 12 years old.

You must use WAS/WERE ABLE TO to describe a special achievement or a single event in the past.

Finally, she was able to visit her birthday place.

You can use either COULDN �T or WASN �T/WEREN �T ABLE TO

for any negative sentence describing past ability.

My friend couldn �t speak Italian.

He wasn �t able to speak Italian.

For forms and tenses other than the present or past, you must use BE ABLE TO .

We haven �t been able to play tennis for a long time

Use CAN and COULD to say that something is possible, to make guesses and polite requests,to make suggestions, and to ask for and give permission.

Could we use our dictionaries?

Can I have five more minutes to answer this question ?

Could you drive me to the hospital, please ?

Maybe we could go to San Francisco.

It could rain tomorrow.

Hope it helps!!

Have a nice day!!