This should be the fastest way to use OCAML / OPAM on windows.
It's a cygwin environment with already installed ocaml, opam, dune (opam), etc.
Just unpack and execute "start.exe"
Integrated development environment for OCaml programming language. It offers a flexible editor with a content type sensitive content assist processor. It provides the possibility to compile and run OCaml projects together with the convenient presentation