Pouco / pouca (in singular) refers to a small quantity of something, poucos / poucas refers to small number of elements. That means that in Portuguese we need only one adjective, whereas in English we need two. If we use pouco in plural it is obvious that we refer to several elements.
amount: pouco singular: Tenho pouco dinheiro. => I have little money.
number of elements: pouco en plural: Poucas pessoas fazem o que é melhor para elas. <=> Few people do what is in their best interest.
On the other side the English little can describe a small amount of something or a small size.
small amount: Querem muita liberdade e pouca responsabilidade. <=> They want a lot of freedom and little responsibility.
small size: Carmo da Mata é uma cidade pequenha em Minas Gerais. <=> Carmo da Mata is a little town in Minas Gerais.
pouco / pouca: describes a small amount of something and is translated with little
poucos / poucas: describes a small number of something and is translated with few
little: describes a small amount of something and is translated with pouco / pouca
little: describes a small size of something and is translated with pequenho / pequenha
Pouco can be used as an adjective (pouco dinheiro = little money) and as a pronoun (Little can be done = Pouco se pode fazer).
pouco little in the sense of a small amount
Pouco dinheiro não é razão para deixar de investir.
Little money is no reason for not investing.
Minha lavadora está utilizando pouca água para a lavagem.
My washing machine consumes little water in the washing process.
pouco few in the sense of a small number of elements
Há escolas com poucos alunos.
There are schools with only few students.
Ela é uma das poucas pessoas que respeito.
He is one of the few persons I respect.
Pouco follows the same scheme as muito, tanto, todo. In plural, poucos or poucas refer to a small number of elements. In singular, pouco or pouca refer to a small amount. It can be used as an adjective or a pronoun. In both cases it has to agree in gender and number with the noun it refers to or, in case of pronoun, with the noun it stands for. With the article o it can be substantivated (The little he knows. <=> O pouco que sabe).
Furthermore pouco can be used as an adverb: Escreve pouco. <=> He writes little.
A little bit of / some can be translated with um pouco de.