Read the source code! Read it again. This is a very concise overview...
1. Make a MODULE\_ENABLE macro flag (io\_cfg.h) -- all of your code should be #ifdef conditional on this flag.
2. Make a file for low-level functions, e.g. user/mything.c
3. Make a file for handling the OSC dispatch, e.g. user/osc\_node_mything.c
4. Define the OSC schema (osc\_schema.c)
5. Add your branch to the root node, conditional on MODULE\_ENABLE (osc\_schema.c)
6. Implement the dispatch method and low-level details.