lot of,lots of,a lot,a lot of有什么区别?

lot of,lots of,a lot,a lot of有什么区别?

a lot是副词
比如说I want to play a lot.
a lot 修饰play
lots of和a lot of是形容词
区别就是lots of既可以加不可数名词 也可以加可数名词
而a lot of只能加可数名词