It sounds like quite a few people have been stumbling when working out the controls, so I clearly didn't write the instructions on the game's page well enough. Hopefully these clarifications will help!
Fort creation is done on a grid: a fort section with battlements appears if that grid cell is completely occupied by damp sand particles. You can get there in a few ways:
- Put both water and sand in your bucket, then dump it in the cell;
- Dump water on a cell that's completely filled with sand particles, damp or dry;
- Damp sand particles fill up the cell by falling down from above, usually when cells are dried out by the sun and things collapse;
- The cell is full of sand particles that are made damp as the tide rises.
The WASD keys in the bottom-left of the screen light up when that key will do something. The colour represents what will be in your bucket if you press it.
To get water, you need to be close enough to the sea level. At the beginning, this means you must be on the beach line.