as a preposition, 'about' is used to indicate the subject matter or topic of something, the movement in or around a place, or to describe a quantity, degree, or manner.
'About' can indicate what something is related to or concerned with. Also, 'about' as a preposition can be used to suggest an approximation.
I read a book about ancient civilizations.
Birds were flying about the garden.
There are about twenty apples in the basket.
When used to indicate approximation, 'about' suggests a close estimate but not an exact number. Avoid using 'about' redundantly. For instance, 'Where is she about?' is incorrect; 'Where is she?' is correct.
as an adverb, 'about' describes the position or movement of something, often indicating that something is in different parts of a place or that it's moving in different directions. It can also indicate that something is near in time or space.
'About' can indicate that something is spread in different parts of a place or moving in different directions. It can also suggest that something is close in terms of time or space.
The children were running about, playing tag.
Winter is about, so we should expect colder temperatures soon.
Is John about? I need to speak with him.
In British English, 'about' can sometimes mean 'around' in the context of being nearby or present, as in 'Is the manager about?' Be cautious not to confuse the adverbial use of 'about' with its prepositional use. Context usually clarifies the intended meaning.