What Google Says:
Organize, edit, and share your photos.
Upload and share your photos on Google+. Tag your Google+ friends and share pictures of them. Transform your photos with 24 new effects.
Source: Google Picasa
Why You Should Use It:
Been using Google Picasa online to back up all my pictures from my desktop – do it! Don’t regret losing all your pictures on your hard drive – back-up now!
If you were using Picasa Web Albums in Picasa, you’ll have noticed that you’ve been transitioned to Google+ Photos now. All your photos will sync to Google+.
Well, here’s a pretty old video from Google, Introducing Picasa 3. I guess they don’t think it needs updating!
And a slightly newer one talking about version 3.5 (they’re at 3.9 now):
Here’s a pretty good video that shows you how to use Google Picasa: