You can't really pick them up and put them down per se. You can add or delete them. As you add, you want to be placing them where you want them to go. If you want to increase the height of a block I believe either the scroll wheel or Page Up/Page Down will do the trick, but you have to press them before you place the block. There is also a Cut/Copy/Paste feature, which is useful for moving or duplicating a set of connected blocks.