Just by doing ordinary, every day activities. The full explanation can be be found by clicking on the banner on the home page.
You cannot. Only Howrse themselves can put items up for sale in exchange for sand.
An Arenophile collects sand
I've heard it costs 500 sand in direct sales, but it might cost anywhere from 5000 sand or up in the auctions. Good luck!
The Sand Horse, AKA Gypse, is a DivineHowrse, Who Turns into Sand Once he Awakens, and His Owner must Rebuild Him. His Owner earns Sand for Rebuilding Him and Sand Can be Traded for Skills. He Can Be Sold nor He Cannot Reproduce. He Comes to Howrse at 42 Yrs Old with a P.Stone, and 200 Skills in Each Category, and a GP of 1200. You Can Buy them in the Autions for 1.5+Million Equus or Rarley in the Private Sales for Max. He Is A Divine!
because the rocks and shells on the shore break down and create sand and then the waves collect it.
That question does not make sense at all.
Assuming you mean the skeleton of a sand dollar after it's dead, no it's not illegal. You can collect as many as you want. I don't think there is a restriction on keeping live sand dollars in salt water aquariums, but they are a shrinking population.
Shells Sand Rocks
No - however sand is able to store energy, in particular solar energy as the sun heats the sand and the sand collects the energy. It may be possible, in future, to try to collect the energy from the sand, but at the moment, this technology is unavailable.
the screen is for putting sand trough and collect small objects in it.
They swallow in sediment collect by their tentacles from their environment, sand and mud.
Because - you can simply evaporate the water by heating it, and collect the water in a separate vessel - leaving the dry sand intact.