How to make stuff in the editor

So, due to a response about my other topic I think I should just post my main question here in a topic.

So, I've gotten to the actual screen where you make your level, but I don't know how to actually put down blocks to make my level. Do I need to buy custom level support for it to work?

Note: the following comes from a guy who doesn't have custom level support. things may or not be correct

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FiNCK editor, unlike KS editor, works with square "Scenery" boxes which can be placed with CTRL+Left Click and re-sized with SHIFT+Right Click. I suggest you to touch in the little ''Help'' button at the left-down corner for more keyboard/mouse comands.

PS: the scenery boxes are supposed to seem like grey boxes and you can't see the actual tiles without testing as seen in this thread