1- Little, a little, the little denote quantity. They are used before uncountable nouns. Few, a few, the few denote number. They are used before countable nouns in the plural number.
2- Little = hardly any. Little is used in the negative sense :
He has little money. (hardly any, no)
A little= at least some ( though not much)
I have a little money in my pocket. We can have chocolates.
The little= the whole quantity, though very little
The little money that I had in my pocket was not adequate to buy ice cream for the two of us.
3- Few = almost none. Like little,few is also used in the negative sense :
My grandparents are usually alone at home. They have few visitors.
A few = at least, some, though not many
It was the Diwali day. So a few family friends came to greet my grandparents.
The few = all of them, though very few :
The few friends who came to meet my grandparents had a gala time with them.