For future ability, both the auxiliaryA helping verb used with main verbs to express mood, voice and tense. E.g.: I can't stand when I am disturbed. ("can", "am") can and the future forms of be able to are used.

If you ask him, he can probably help you. 
If you ask him, he will probably be able to help you.

To express that someone has the power or skill to do something, the auxiliaryA helping verb used with main verbs to express mood, voice and tense. E.g.: I can't stand when I am disturbed. ("can", "am") can and the semi-auxiliary be able to is used.

I can swim.
We can't enter this street because it's blocked.
I am not able to help you at the moment.

I could swim when I was 5.