Photo Stream is a separate album stored on iCloud that keeps your last 1000 photos (no videos).
iCloud Photo Library is (will be) your entire photo library (with videos) stored on iCloud.
Photo Stream is a separate album stored on iCloud that keeps your last 1000 photos (no videos).
iCloud Photo Library is (will be) your entire photo library (with videos) stored on iCloud.
You access them with any iDevice or Mac with iCloud Photo Library turned on. It will also be available on Windows and the Web according to the Apple website.
"iCloud Photo Library keeps your photos and videos organized into Moments, Collections, and Years across all your iOS devices and even on the web. You can mark favorites, create albums, or drag photos into a custom order whether youre on your iPad, iPhone, or iPod touch."