As a new developer, it can be daunting to understand and learn all of the technologies used in OED. This page, which everyone is encouraged to update, contains some resources that can be useful in this pursuit. This is not meant to be an exhaustive list nor rate these sites but to provide ones that project members or others have found useful. As always, you can contact the project with questions or for help.
The following graphic shows some of the main technologies in OED grouped by where they are used. The "Others" group are technologies that generally span multiple parts of OED and are seen depending on what you are doing. Developers often only need to know the technology in one area or even a subset of that area. This can make the task of learning the needed technologies much more manageable.
You may also find the Technology Overview giving an overview of the front-end process to be useful.
For several reasons, OED uses the PostgreSQL database. While much of database code is standard SQL, some is PostgreSQL specific to access specific features.
OED uses the Chai and Mocha testing frameworks to test the OED code base. Both sites have information on usage as well as many other sites. We generally only use a subset of the features that can be seen by looking at our test code.