Could any one enumerate some applications of enumerative combinatorics and Ramsey theory in TCS? The combinatorics, needless to say, is very closely related to TCS. But I found it hard to find the applications of enumerative combinatorics or Ramsey theory.

Or rather than being applied to TCS, the enumerative combinatorics or Ramsey theory is related to TCS because we use TCS techs and algorithms to tackle their problems.

I dont know very deep theory works, so please treat it easy.
This book will be helpful:

http://books.google.co.uk/books/about/Extremal_combinatorics.html?id=g6X2VWuB8qIC