‘Can’ or ‘be able’?

Can and be able often mean the same: ability.

Example:

Some people are able to/can walk on their hands.

So when do we use can and when do we use be able?
We use can to mean ‘know how to.’ We use it to mean what people or things are able to do (or unable to do) because of their knowledge, skill, strength, nature, design etc. And also in expressions like can see, can hear.

Example:

Can you drive? (more natural than Are you able to drive?)
Roses can grow anywhere. (more natural than Roses are able to grow anywhere.)
I can see a ship. (more natural than I’m able to see a ship.)

Be able is used in cases (e.g. future, present perfect) where can/could is not grammatically possible because it has no infinitives or participles.

Example:

One day scientists will be able to find a cure for cancer. (not One day scientists will can find a cure for cancer.)
What have you been able to find out? (not What have you could find out?)

Also, able is not often followed by passive infinitives.

Example:

He can’t be understood. (more natural than He is not able to be understood.)