Oppia can be installed on your machine running Linux, Mac OS or Windows. Or if you want to ensure that you always have a clean machine identical to other developers, you may want to install Oppia through Vagrant. Vagrant will also provide isolation between your host machine and things that Oppia needs to install and change, or allow you to build different development versions of Oppia on different branches.
If you just want to create and share explorations, you may be able to use the hosted server at https://www.oppia.org (in which case you don't need to install anything).
Please refer to CONTRIBUTING.md.
(Basically, start by forking the Oppia project on Github, then creating your changes against our develop branch, and finally send us a pull request)
Also, don't be discouraged if you're new to "open source", or if you're still a student -- many of our contributors are, too. The main thing is that you care about helping more people around the world to learn things better. We'd also be happy to provide mentorship and support if this is your first time contributing to an open source project.
There are 3 types of tests which are carried out - Server Side, Client Side and End to End tests. Thes tests help to ensure that the code is in a working state. Before checking in any commits to the Oppia repository, please ensure that every single test passes. For information on running the tests, please refer to Running Tests wiki page.
If you run into any problems, please read our Developer Wiki, or file an issue on our issue tracker, or post to our developer mailing list. Or you could probably ask your questions on our official Gitter or IRC channels preferably during the following office hours (in UTC):
Tuesday -- 08:30 - 09:00, 21:30 - 22:00, 00:30 - 01:00
Wednesday -- 16:30 - 17:00, 21:30 - 22:00, 00:30 - 01:00
Sunday -- 16:30 - 17:00, 21:30 - 22:00, 00:30 - 01:00