"Cosmos" is a typical pop-science book - scientific information is explained in "simple reader" language, not expecting any background whatsoever. This is, accidentally, one of my favorite types of books :-)
The focus in this book is on astronomy - how big is our universe, how old it is, how it "works", etc. Sagan pays a lot of attention to stars and galaxies, but also presents the more advanced topics of black holes and pulsars. There are also occasional earthly detours - evolution of life on earth, ancient greeks, the library of Alexandria, voyages of explorers, etc.
The book also tries to bring up some philosophical questions, especially in relation to the possibility of other civilizations in the cosmos, and how a contact between us and them would happen.
"Cosmos" is very well written, reads like a mystery novel and is a great source of interesting information. This book could have easily been twice as long and it wouldn't tire me. The only downside is its being a little outdated (1980).
Highly recommended.