What are the differences between "waterfall", and "series", methods in the NodeJS async library?

I am just getting started with the async npm package to re-write, and then extend some code that is rotting in callback hell; just came here, to know if anyone can quickly give me a difference between the async.waterfall, and async.series methods; both of them look almost the same to me? Also, can I have a async call inside another async call? Thanks in advance!