Photo Stream is iCloud image backup and distribution component. Take a picture (or screen shot) on your iPhone, iPod touch, or iPad, and -- when you're on Wi-Fi -- iCloud will store a copy of that picture on Apple's servers and push copies down to all your other iOS devices, as well as your Mac and/or Windows PC. On iPhone, iPod touch, and iPad, iCloud will store up to 1000 photos, or 30 days of photos. On your Mac and/or Windows PC, iCloud will store all your photos. Photo Stream will also let you view your photos on the Apple TV.
With Photo Stream, any picture you take with your iPhone, iPod touch, or iPad is automatically stored on iCloud and pushed down to any other device logged into your iCloud account. Photos are only transferred when you're on Wi-Fi
Once you've enabled Photo Stream on your iPhone, iPod touch, and/or iPad, you'll be able to see any pictures taken on any of your iOS devices, on all of your iOS devices.
Photo Stream only stores and pushes photos when you're on Wi-Fi. So, if you don't see your latest photos, make sure you connect your device(s) to Wi-Fi and wait a few moments.
Your Apple TV can wirelessly stream all the pictures from your iPhone, iPad, and iPod touch. It's a great way to share pictures with friends and family on right on your home television.
iCloud will start to populate your Photo Stream on your Apple TV. Depending on the size of your Photo Stream and the speed of your internet connection, it might take a few minutes.
Photo Stream, like the rest of iCloud, is built right into OS X Lion on the Mac (or the Mountain Lion developer preview). You can access it from within either iPhoto or Aperture.
iPhoto will start to import your Photo Stream photos. Depending on how many photos you have, and how fast your internet connection is, it might take a while.
Apple's higher end photo editing app, Aperture, can also be used with Photo Stream.
If you've got a Windows PC, you can enable Photo Stream through the iCloud control panel.
Your Windows PC will start to import your Photo Stream photos. Depending on how many photos you have and how fast your internet connection is, it might take a few minutes.
If you have personal, private, or any photos you simply don't want to be stored on Photo Stream, you can delete them from iCloud without deleting them from your device.
Again, this will only remove the photo from Photo Stream, not from the Camera Roll of the device with which you originally took it.
If you still need help with setting up or using Photo Stream on your iPhone, iPod touch, iPad, or Windows or Mac PC, or any other iCloud feature, head on over to our iCloud Forum and ask away!
Ally Kazmucha, Chris Oldroyd, and Gary Mazo contributed major sections of this guide.