“Able” is an adjective that should only be used for living things (mortals and animals).
So humans are able to do things (poder hacer algo o saber hacer algo). Here are two examples:
- Alejandro is an able student
- Sanchez is not an able politician
“Able” can also mean “capaz” as in this example:
- Alejandro is one of our ablest students (Alejandro es uno de nuestros alumnos más capaces).
You should not use “able” for things. These examples are incorrect:
- Alejandro´s Porsche is able to go very fast.
- This computer programme may be able to calculate the answers.