Four steps
Install it. Play.
01
Download the installer
The button above gives you SourClient-Setup.exe. Your browser will put it in your Downloads folder.
02
Run it
Double-click it and follow the installer — a few seconds, and the launcher is in your Start menu.
A blue “Windows protected your PC” box is SmartScreen not knowing a new publisher yet: More info, then Run anyway.
03
Sign in with Microsoft
Open the launcher. It shows a short code — enter it at microsoft.com/link with the account that owns Minecraft: Java Edition. It happens on Microsoft's own page, and we never see your password.
04
Press Play
The first launch downloads 1.8.9 and sets up your profile, which takes a minute or two. After that it starts in seconds. Then tune your HUD, pick a cloak and set your keybinds.