The controls in Eaglercraft 1.8.8 are designed to be intuitive and match the official Minecraft layout, making the transition seamless:
At its core, the is a recompilation of the actual Minecraft Java Edition source code (specifically version 1.8.8) into WebAssembly and JavaScript. In layman's terms, a developer named "Lax1dude" and a community of reverse engineers took the original game logic and translated it so it can run inside the sandbox of a web browser using HTML5 and WebGL.
The most impressive technical feat is multiplayer. Eaglercraft does not connect to normal Minecraft servers directly. Instead, it connects to or uses a proxy that translates vanilla server traffic. The 1.8.8 client is compatible with thousands of public Eaglercraft servers worldwide, many of which run custom plugins, Factions, Skyblock, and KitPVP.
Eaglercraft is designed to be a "bring-your-own-asset" project in some configurations, but most public, freely accessible clients are aimed at providing a legal way to play the game in the browser.
If you're ready to dive in, there are a few ways to get the client, depending on your technical comfort level.