Paint can look like beach sand by stippling 1 or 2 colors over a base coat. This would be a light tan with a darker tan mixed with glaze stippled over it. A third darker color can be added (stippled) for a varied effect.
An alternate approach would be using a faux sand paint. This can also be used for the base coat for a textured feel with the stippling on top.
The 'ocean' will take some experimenting to figure out. Painting water will take artistic expression and some skill. Here's a video that shows <a href="https://www.house-painting-info.com/how-to-paint-water-on-walls.html">how to paint water on walls</a>.