The use of "a few" and "a little" depends on nature of the following noun, that is, if the noun is countable, "few" is used. On the contrary, if it´s uncountable, "little" is the correct one. Remember countable nouns are those which can be counted and therefore, they have singular and plural forms. On the other hand, uncountable nouns cna´t be counted and they always appear in the singular (they don´t have plural forms). As you know, "little" and "few" can appear without article "a/an" and when this happens their meaning changes.
Let´s do some exercises!
Exercise 1
Exercise 2
Exercise 3
