Picasa is a digital photo & video organizer designed to organize and edit digital photos and videos. Picasa allows you to organize, edit and share photos online. Photos you upload to Google+ will be automatically resized to 2048 pixels and stored for free. Picasa Web has a video upload limit. Uploading videos upto 15 minutes or less is free.
Here are steps to share photos from Picasa web:
1. Go to https://picasaweb.google.com/ & sign in to your account.
2. Once you have signed into your account, click your album which you want to share.
3. Click "Share" button located on right side of the window.
4. A pop-up window "Share on Google+" opens up.
5. Add a comment if you would like to add context to your photos.
6. Add names, Google+ circles or email addresses to share your photos.
7. Click "Share" button.
8. All your photos will now be shared.
You can install PicBackMan's Picasa uploader for Mac from the website and start backing up photos and videos.