Randomizing And Resetting
Near the right of the screen, you'll see a cluster of buttons. These will do various things and then automatically submit the form for you as well.
Randomize Ratios
This setting will randomize everything in the Terrain Generation Ratios cluster of settings. This can have a pretty dramatic effect on the way terrain generates, while keeping the Map Size, Generation Rounds and Continent Sculpting the same.
By clicking the "ΓΈ" symbol on a ratio you can lock that ratio in place so that "Randomize Ratios" doesn't affect it. This can be very useful to allow you to randomize some settings while keeping other ones that you like the look of intact.
By default, "Ocean Ratio" and "Land Spread Ratio" are automatically locked in place because changing them can have some dramatic effects on the shape of landmasses. You can however unlock them like any other ratio.