There are several ways of setting up your workstation for Joomla! development. Some suggestions can be found at Setting up your workstation for Joomla development.
There are many articles, tutorials, references and FAQs which focus on component development. If this is your first time developing a component for Joomla, you should start with the Absolute Basics of How a Component Functions. If needed, you can visualise the control flow of a component with these diagrams.
The following articles will help familiarise you with Joomla! plugins. They are a good starting point to understanding and then developing plugins.
Accessibility is a priority for Joomla across its CMS, front- and back-end templates, and community extensions. Explore Joomla’s accessible UI library and best practices.