The first thing you want to do is learn where the main files are.
o.c -> Main Parser & REPL
static/ -> HTML Pages w/ JS
docs/ -> ReadTheDocs Pages
When you create a PR, the build will be run through Travis and Heroku. Your PR's app will be in the format o-lang-pr-#.herokuapp.com, where you can test out the IDE.
Please create an issue with a decent title and a description of your problem with steps to reproduce it and a link to the WebIDE.
If you have an idea for a new feature, but have no idea how to Java, you can create an issue detailing how your feature would work with examples.
When adding a new feature, please thoroughly explain what it does and how it can be used effectively with examples from the current WebIDE or your PR's.
Ex:
My pull request adds a + operator that will pop two numbers off the stack and push their sum. Example
>>> 1 2 + o
3
>>> 5 2 6 + + o
13
I believe by addition to O will be good for golfing because adding two numbers together is usually pretty useful when golfing.