First, get the Java Development Kit for Java version 8, go to:
We're interested in the stuff in the first gray box. You'll need to accept the license agreement, and choose the appropriate download for Windows/Mac/etc. Unless your computer/OS is very old, you probably want the 64-bit (x64) version, not the 32-bit i586 version.
Download & run the installer.
Eclipse for Windows:
Second, go to https://eclipse.org/downloads/packages/release/Mars/2 and download the "Eclipse IDE for Java Developers" for your operating system. (Again probably choose 64-bit, unless you went with 32-bit Java above.).
After you download the zip file right click and "extract" it to "C:\", which should create a folder "C:\eclipse". Then you can create a shortcut to the "eclipse.exe" file on your desktop by "right-click dragging" the "eclipse.exe" file from C:\Eclipse onto your desktop.
(A step-by-step guide for Windows is available here: http://www.wikihow.com/Download,-Install,-and-Run-JDK-and-Eclipse , but it doesn't describe how to make the shortcut for handy use later.)
Eclipse for Mac:
Download the "Mac Cocoa" link for the "Eclipse IDE for Java Developers" here: https://eclipse.org/downloads/packages/release/Mars/2
Continue with steps 4-7 on this page: https://beginnersbook.com/2016/04/how-to-install-eclipse-on-mac-os-x/
If you run into trouble, drop by my office (or ask a tutor), and we can help!