How exactly do I place blocks in creative?

Quote from Whip

So I picked a block, then I set starting point, then an end point. And nothing happens. I have all of my key binds custom but nothing seems to work including action key and secondary key.

You need to have the block in your top bar and in your hand then use your mouse to click the start point hold down the mouse button and move your mouse to the end point , then click the other mouse button.

Quote from Whip

Okay so "placement" (option F6 in creative) doesn't do anything then?

as far as i know that does not work yet, unless Red51 has just updated it

If you want to place blocks in big areas then ATM the Block Placer Plugin is your only option

you will need to copy that plugin into your plugin folder then select your area and in chat type /place block 23 or what ever the id is of the block you want