The more you read this book, the more you're going to like OCaml...it's a really nice language -:)
The book covers the basics like Lists and Patterns, Records, Variants and Error-Handling. But of course it goes beyond with Functors, Objects and Command-Line Parsing...not letting important concepts like JSON handling Concurrent Programming aside. So...it's a pretty complete reference to start out.
By the way...the book is 509 pages...so it's pretty long...but full of examples and demonstrations...
Here's a little code that I wrote to flat out lists -;)
open Core.Std let rec flat list = match list with |  -> "" | head :: tail -> head ^ (flat tail) let () = printf "%s" (flat ["1";"2";"3"])
Here's the result...
As you can see...OCaml is fun...so go ahead...read this book and expand your knowledge -;)