A/an is the indefinite article (singular).  Some/any is often used as the plural

The

'Theยด is called the definite article, and can also be used for the plural.

About can be used with the Infinitive means to be doing something very soon.  It will happen imminently.

 

'About' is used to discuss ordinary things.  It covers general issues.

The 'infinitive' is the 'base' form of a verb.

 

It usually includes 'to'.

 

'Able' is used in the structure 'be able + Infinitive'.