The first row has scroll lists for up to three Chain Rings (20 to 62 teeth) - leave unwanted values at zero. It also has a scroll list for the wheel diameter in inches or centimetres. The second and third rows have scroll lists for up to 9 Free Wheels (12 to 32 teeth) - again, leave unwanted entries at zero.
The next two rows summarise the selected gear and wheel sizes, and have the radio buttons to select Metric or Imperial measurements, and whether gear pairs leading to extreme chain angles are suppressed.
The lower section has the Gear Inches/centimetres and other information for the selected Chain Rings and Freewheels. The rows are in ascending order of Gear Inch/centimetre. The entries in the CRxFW column are indented to show gear changes requiring Chain Ring shifts
The columns are as follows:
Barry Masterson has produced a form-based calculator (set up gear values, submit them then get a list of Gear Indices etc in return) here. It also has metric and extended versions. My Java version has some visual similarities to Barry's, but the underlying code is completely distinct.