Before you start installing Eclipse, make sure that you have the Java Development Kit (the JDK) installed on your system. If you're not sure, it's safe to just try installing it again. (If you already have the JDK installed, installing it again will just update you to a slightly newer version.)
To download the JDK, go to this page and download the appropriate file for your operating system.
Note: while the latest version of Java is Java 9, we strongly recommend you use Java 8 in this class. While our course projects in theory work with Java 9, they have only been tested with Java 8. The link above will take you to the Java 8 download page.
NOTE: if you used Eclipse before, you may have an older version installed. If so, we strongly recommend you uninstall it and install the latest version for maximum compatibility.
You can download Eclipse at eclipse.org/downloads. The latest version, as of time of writing, is Eclipse SimRel.
Run the Eclipse installer. You should see a window like the one below; Select the first "Eclipse IDE for Java Developers" option.
After that point, you can keep hitting "yes" and select all the default options (unless you want to change something).
You should eventually see a screen like this. Click the "Launch" button.
When you run Eclipse, it'll ask you where you want your workspace to be (see screenshot below for example). Your workspace will be the location where Eclipse will add any new projects you create. You can change the location of the workspace if you want: just make sure you remember what you picked.
Once you're done, you should see a "Welcome" screen like below. Close the "welcome" tab to open the regular editor.
Next, select "Windows > Preferences" (PC) or "Eclipse > Preferences" (Mac) in the menu. Then, select "Java > Installed JREs":
Click the "Search" button and select the "Java" folder. This folder should contain your installed JRE and JDK. (If it contains only the installed JDK, that's also ok). You can probably find this folder located at:
C:\Program Files\Java
/Library/Java
For example, on Windows:
After hitting "ok", you should see a screen with a line for either both the JRE and the JDK, or just the JDK. Select the line for the JDK:
Click the "Apply and close" button.
Eclipse, by default, contains a fair degree of clutter. If you want to minimize the clutter, feel free to close the "Task List" and "Outline" tabs/views to the right.