Sorry if someone already answered it, but the editor is completely used by the mouse. Hold down left mouse button to draw, hit Enter to see what the world would look like (doesn't show evil/good/etc, or snowy/...not, and obviously it doesn't show caves, you can't place those yourself, however that would be a cool idea...). Hold down the right mouse button and move the mouse to navigate the world (fun
), and you can basically left click on any text to edit it. For example, painting/not painting, normal vs. blending or w/e drawing, edit drawing size, view a certain map (temperature, savagery, volcanism, elevation, drainage, and rainfall), and edit what value each will do (click on the numerical drawing value for rainfall, for example, and type in what you want to draw with, then hit enter). There might be more, but that was just a quick browsing of it by me.
Also, it may have just been me who wasn't quite sure at first, but if you are trying to get a certain tile (ex. - swamp, forest, hills, etc.)...
rainfall goes from 0-100, with 0 making dry areas
elevation goes from 1-400 (not sure what the second number means...), with anything below 100 being water, and with 300+ being mountain
temperature goes from 25-75, and has no effect on the land (besides snowy/not snowy, but that cannot be seen from the editor)
drainage goes from 0-100, with 0 making areas that retain water, such as swamps and deserts, and 100 making areas that lose any rainfall that comes, such as forests and badlands.
savagery goes from 0-100, and also has no effect on the land, but might affect evil vs. good, but I haven't tested it
volcanism goes from 0-100, with 0 never having volcanoes and 100 always having them, unless a maximum is otherwise specified in the advanced options, or so I think, maybe just a high chance. I made many tiles volcanoes in the editor, maybe 100 or so, but only turned out with 25 or so when the world generated. Maybe a bug?
EDIT: gramer and something I misread