The Shattering of Adonalsium was the major event to occur within the Cosmere, during which were created - specifically - the 16 Shards, which were taken up by 16 people. Hoid was witness to it, though whether he simply observed it or caused it remains in question. Be that as it may, the event was intentional. Whether the intent was malevolent or otherwise also remains in question.
A. Some planets had people before the shattering.
Q. Before Adonalsium was shattered, was there magic in the Cosmere and what form did it take?