If your project depends on the external libraries, you should first install them with opam.
Assuming your dependencies are foo and bar and the main entry point of your project is foobar.ml you can then build a bytecode executable with
ocamlbuild -use-ocamlfind -pkgs 'foo,bar' foobar.byte
Warning: the names foo and bar must be the names of the ocamlfind packages, they may differ from the names of the opam packages.
Instead of specifying the packages on the command line, you can create a config file named _tags with the following content
true: package(foo), package(bar)
If your project has no external dependency and has foo.ml as its main entry point, you can compile a bytecode version with
ocamlbuild foo.byte
To get a native executable, run
ocamlbuild foo.native