Apex is like Salesforce’s secret sauce - the language that enables custom features and automation within their cloud platform. With a Java-like syntax and database-procedure-like capabilities, you can write code that responds to everything from button clicks to data updates.
What makes Apex unique is that it runs directly on Salesforce’s servers, letting your code integrate tightly with the platform’s ecosystem. Keep in mind there are so-called "governor limits" - restrictions designed to prevent any single tenant from consuming all resources - so you need to write efficient code.
If you want to dive deeper, there are plenty of resources such as Apex Recipes on GitHub with examples and best practices. Apex may not be widely known outside the Salesforce world, but for developers on the platform it’s an indispensable tool.