'A first hour with OCaml' says, at the beginning: > You may follow along with this tutorial with just a basic OCaml installation, as described in Up and Runnin

'A first hour with OCaml' says, at the beginning: > You may follow along with this tutorial with just a basic OCaml installation, as described in Up and Running. So, you can't really skip 'Up and Running'. And, the Graphics module usage is in the section 'A module from OPAM', which explicitly talks about installing the package and then loading it in the REPL ('top level').