These are quantifiers: words that tell us how much or how many of something there is. Choosing the correct quantifier depends on whether the noun is countable or uncountable and on the meaning you want (small amount, large amount, enough or not enough).
Use many with countable plural nouns: many documents, many clients.
Use much with uncountable nouns: much time, much information.
Use few / a few with countable nouns to express small quantity (few = negative idea, a few = positive).
Use little / a little with uncountable nouns to express small quantity (little = negative idea, a little = positive).
Use a lot of and plenty of with both countable and uncountable nouns to indicate large quantities (plenty often implies enough).
Table
Quantifiers: Usage and Examples
Quantifier
Used with
Example
many
Countable plural
There are many applicants for the position.
much
Uncountable
We don't have much time to finish the report.
few / a few
Countable plural
Few employees attended the meeting. / A few employees arrived early.
little / a little
Uncountable
Little progress was made. / We have a little information to share.
a lot of / lots of
Countable & uncountable (informal)
The team has a lot of experience. / There are lots of files to archive.