A long time ago 'persons' was used instead of 'people'. While 'persons' is still used in some set phrases, the plural of 'person' is now commonly known as 'people'.
E.g. "Today a person asked me if I know where the bank is".
"Today 10 people asked me if I know where the bank is".
Remember, people is plural so you cannot say 'a people asked me'.
Only use 'a' or 'an' before singular countable nouns.
There are a number of common language difficulties in English. The posts on this page are designed to give you answers to some (if not all) of these problems.