To find your User and Album ID, you should open the album directly from the Google+ or Picasa page. When the album comes up, you will see the user and album ID in the URL. Any album you want to display with this plugin must be marked for "Public" sharing from Google.
Max Image Size - The maximum width, in pixels, of photos. A value of 100 will produce square thumbnails.
Max Results - Max number of photos to show from the album.
Randomize Photos - Randomize the order that photos are displayed in.
Show Caption - Show the photo caption, if available.
Link to Album - Link the photos to the Google album page.
Slide Duration - Time to show each photo before advancing.
Fade Speed - Fade in / out transition speed between photos.
If you are trying to display an album that is shared with "limited" visibility, then you will need an authkey. You can learn more about them here.