In my opinion, this visualization is not particularly compelling if you don't already know what you're looking at, and I can relate to your sentiment of confusion.

This is a tool for analyzing and comparing differences between drivetrain setups. A bicycle drivetrain is typically composed of a single gear, or two or three gearing choices "up front" (on or near the crankset) and either a single-speed "rear", or anywhere from two to 30 (!) [1] selectable gears at the rear hub.

The various "output" modes from this tool are all derived from the Gear Ratio, usually simply the ratio of the number of teeth "up front" to the number of teeth "in back" for any given selected gear.

By entering multiple drivetrain setups, you can quickly compare overall range between different drivetrains. You can also see the "steps" between different gears within a given drivetrain, which tells you how many pedal cadence choices you'll get within a given comfort zone for the bike's intended riding purposes.

[1] SRAM's DualDrive 3x10 internally-geared hub with a standard cassette and derailleur.