If a noun is in singular, we use a little
a little money
If a noun is in plural, we use a few
a few friends
Countable nouns have a singular and a plural form. In plural, these nouns can be used with a number (that's why they are called 'countable nouns'). Countable nouns take a few.
4 friends – a few friends
Uncountable nouns can only be used in singular. These nouns cannot be used with a number (that's why they are called 'uncountable nouns'). Uncountable nouns take a little.
3 money – a little money
WITHOUT THE ARTICLE
a little = some
little = hardly any
I need a little money. - I need some money.
I need little money. - I need hardly any money.
a few = some
few = hardly any
A few friends visited me. - Some friends visited me.
Few friends visited me. - Hardly any friends visited me.
Without the article, little / few sound rather formal. That's why we don't use them very often in everyday English. A negative sentence with much / many is more common here.
I need little money. = I do not need much money.
Few friends visited me. = Not many friends visited me.