Hey, thanks Camh! :)
Some of the screenshots are from later parts of the game, not featured in the demo. In the final version you will be able to find tools that allow swimming, breaking the super blocks and other actions.
Although you can't do all these things yet, you get a special message if you find all available items in the demo, so you'll know when you have found 100% of them. Some of them are pretty hard to find, though!