"Unix System Programming with Standard ML" by Shipman clarified a lot of "how the rubber meets the road" for me. Free download at http://www.mlton.org/References.attachments/Shipman02.pdf . Although unless you're using SML/NJ, the Concurrent ML examples would have to be adapted.
Is there something similar for OCaml? I skimmed https://caml.inria.fr/pub/docs/oreilly-book/html/index.html , but I'm not as au-fait with the OCaml ecosystem so would appreciate a pointer to something more up-to-date.