Fog of Dota can only read public games. You turn this on once, in Dota on your computer.
In Dota it looks like this
Your newest games show up within minutes. Older games follow while OpenDota reads your history, usually within the hour. The oldest games may not show up.
Your games, with your account, on Fog of Dota and on sites like OpenDota, Dotabuff and STRATZ. Your Steam profile and friends list stay as they are. You can turn it off again at any time.