Official timeline (for those confused about the sequence of events) [Spoilers]
Here's an official timeline released by Netflix:
https://i.imgur.com/WzIJSp6.jpg?1
By the end of the last episode you should have a reasonably good picture of what's happened, and where it all fits, but this is nice as it lays the whole timeline out for you with illustrations. Including the year - on what calendar, I have no clue. The Witcher takes place on a land mass they call The Continent, which is clearly not any of ours, so this world isn't Earth. Like Middle Earth or Westeros it's ... elsewhere.