Hit play and pause (in the bottom left) to see the simulation run. Notice how the box does not move? This is because it's mass is set to 0. You can play around by selecting and duplicating the objects - this world is not persistent so your edits won't be saved.
Check this out! The ocean shader is an entity that implements something called a "projected grid". Select the OceanShader from the "Hierarchy" tab on the right, open its "Properties" tab, and play with the settings!
Check this out - It's a non-persistent blank space. It's marked for anonymous use and single player. This means that anyone can mess with it, but you won't see other users in the space with you. It will also reset to blank when you leave.