The known world is limited. There is one known large continent and several islands around it.
This continent is divided into different countries - with an Empire in the center. As the stereotypic stories go, the emperor dies and is taken over by his grandson, who's become greedy and mean. He starts reaching out to the other countries, raiding the towns and villages, killing people.
It seems he can't be stopped, so people start fleeing to the islands around - but some miss their targets due to storms or unability to navigate the high seas. They drift off and most of their ships get wrecked.
You were on one of those ships and most likely got washed up on a beach of an uncharted island...back up!