The usage of ‘many’, ‘much’, ‘few’, and ‘little’ as a pronoun

People is usually the plural form of person:

One person, two people, three people, ...

What you'll notice here is:

• People is countable.
• People is plural, even though there's no -s suffix.
• The singular form is always one person, never *one people.
• The indefinite forms include a person and people.

Here are a few more details you can safely ignore:

This is called suppletion, and it's much like how we say went as the past form of go, even though went was originally a different word (the past form of wend).

The plural persons exists too, but it's limited to a few formal legal contexts. In everyday life, people use people as the plural form and ignore the word persons entirely.

And now, here are some details you shouldn't ignore:

People isn't just used as the plural of person. It's also used as a separate word meaning "the persons living in a country and sharing the same nationality" (Collins). And when it's used in this sense, both the singular and plural forms look different:

One people, two peoples, three peoples, ...

Although these are grammatical, we're not terribly likely to count peoples this way. This term is more likely to be used in phrases like the French people, the Navajo people, or the Native American peoples (note the plural, as there is more than one group of Native Americans).

You can tell the difference by how the word looks. If it's two people, it's the plural of person. If it's two peoples, it's referring to two groups of people, each of which has a distinct identity. And if it's one people, it must be referring to a group.

But most of the time, people is the plural of person.

'Few' is mainly used when talking about the number of 'count nouns', such as 'dogs'. You can say

Few dogs make good friends with cats!

to mean that not many dogs make good friends with cats. But if you said

Little dogs make good friends with cats!

this would suggest that dogs that are small (cat-sized, perhaps?) make good friends with cats.

On the other hand, 'little' is used when talking about the amount of 'mass nouns', such as 'water'.

There was a flood, but little water actually got into the house.

means that not a lot of water got into the house (thank goodness!). On the other hand,

There was a flood, but few water actually got into the house.

is not a valid sentence.

Sometimes you can use either to produce equivalent sentences, but usually 'few' will precede a plural noun and 'little' will proceed a singular (mass) noun. For example:

John had little reason to dislike Jim.

Jim had few reasons to dislike John.

Both of these sentences mean that they haven't given the other much cause to dislike them.

A little and a few both mean some, but the above rules still apply here. So you would say a few dogs and a little water, but not a little dogs or a few water (which aren't valid sentences).