Which JDK should I download for Windows 10?

In a browser, go to the Java SE Development Kit 10 Downloads page and click Accept License Agreement. Under the Download menu, click the Download link that corresponds to the .exe for your version of Windows. Download the file jdk-10.

Which version of JDK should I use?

While you’ll see earlier versions of Java (5,6,7) in the real world, remember that 8 is the actively supported version today. You’ll want to install the JDK if you want to write and compile your own Java applications but the JRE is all you need to run existing Java apps.