You can create an API key from inside Emby at Settings > Advanced > Api Keys.

As of v0.6.11 the widget supports fields ["movies", "series", "episodes", "songs"]. These blocks are disabled by default but can be enabled with the enableBlocks option, and the "Now Playing" feature (enabled by default) can be disabled with the enableNowPlaying option.

  type: emby
  url: http://emby.host.or.ip
  key: apikeyapikeyapikeyapikeyapikey
  enableBlocks: true # optional, defaults to false
  enableNowPlaying: true # optional, defaults to true