A lot用在句末,比如Thanks a lot
A lot of=Lots of,形容很多,不可数名词和可数名词都可用.
Few 可用作限制形容词,表示很少：He has very few(=not many,a small number of)friends.也可用作补语：These trees were few and far between.还可以用作代词或名词：Many students took exam,but few passed.
A few 可用作限制形容词,表示几个,少数：Are there any streets in this village?No,there are none,but there are a few paths.
A little 表示有一点（肯定）,而little表示很少（否定）.A little 可用作限制形容词,修饰名词："Have you much food to spare?""No,I have little=(not much).""Have you any food to spare?""Yes,I have a little(=some little,some) food.也可用作代词或名词,还可用作副词.