In addition to the built-in Odoo modules and the various settings that can change the way Odoo functions, there is also a growing collection of custom Odoo modules written by the community. When you find a business requirement for which you believe you may need to do some custom module development, take the time to go to the Odoo application repository and search for modules that could perhaps fit the purpose. Even if the module is not exactly what you are looking for, there can often be a lot of valuable code in those modules that can help you with your own module development.

Even more importantly, these applications are invaluable for studying how to build and customize applications in Odoo. When you get stuck trying to solve a development problem, the Odoo source code and the available applications that you can find in the Odoo application repository are often all that you need to find the solution.

In Odoo development, we can sometimes refer to custom applications and modules interchangeably. For the most part, modules are customizations that extend Odoo applications with additional functionality. Odoo applications would typically add an entire new set of features that would be more substantial than a module. There is, however, no real difference between them in how you approach development. Both are created in the same way.