How do you even start when the opener is just 'start wherever'?

The whole premise is three continents, twelve species, plus whatever mythical stuff isn't in the main list, and then the opening line just says start wherever you want. I like open sandboxes in theory but I never know if I'm supposed to invent my own character and location from scratch or wait for some kind of prompt. Do people usually just declare a species and a continent in their first message and let it build from there, or is there a better way in? Genuinely asking because I've stalled out on the first line twice now.