If you click on News, you get a quick overview of recent activity.
Your Space shows you who liked and commented on your stuff
Your Visitors shows who on your contact list dropped by to, well, visit
Your History is where you find your comments on other people's photos, and replies

If you click on Photos, you can see your photos in nice small thumbnails. On a contact's page, you can do the same - the little blue arrow banner on the menu tells you who's photos/albums/articles etc you get to see if you click on it. Nice thumbnails, goooood thumbnails... :)

Albums shows your albums again in nice thumbnails. When you open an album, you have an option to upload directly to it (like Photobucket).

In both Photos and Albums, you can control the size of the thumbnail display, and both give you a Lightbox option (like Flickr used to).

To add a photo to a group, look for the group icon in the arrow bar that shows the favorite star and facebook sharing options. The group icon shows three little heads and a + sign. This will add the photo to the group.

Embed codes are only available for Club members, so you can't embed your photos elsewhere like you can/could on Flickr free and Photobucket free (although Photobucket only lets you embed either thumbnails or the full size image, whereas Flickr and Ipernity Club allow a choice of sizes, from what I know of the Club level).

That's what I've learned so far, feel free to add more!