Able = Having the power , means or opportunity to do something.

• Will you be able to come?
• They need to be able to irrigate without relying solely on rain water.
• He has informed his ability to attend the meeting.

Capable = Having the ability or fitness or quality necessary to do or achieve a SPECIFIED thing.

• Show your teacher what you are capable of.
• He is quite capable of taking care of himself.
• Only the democratic party is capable of running the administration.
• Automation gives us the capability to do certain jobs quickly and well.
• A very capable doctor/nurse/teacher.
• I think your plan is capable being improved.
• We have to further improve our nuclear capability considering the local situations.