Use the number keys 1-3 to select a tool (Pickaxe is used to remove blocks). Any modifications you make will be uploaded to the SCRATCH SERVER after a short delay. Click on a block to use your Tool on it or place a block there. Press SPACE BAR to view higher building places, and click while pressing space to build upwards. There is a max of 3 layers of blocks due to the amount of clones possible. (Maybe this will be fixed).
Not working for you? That means you are a N00B, and have not achieved FULL SCRATCHER STATUS, which is needed to save cloud variables. Not saving your buildings? This calls for a FULL RESET, just press R. This resets the world to its default "OCD Perfection" landscape. Also Note: You cannot see other players on-screen. Any building that is done by another player while you are playing won't show up on your screen until you re-load the world again by clicking the green flag.