Windows 10 adds a new 'Share' button in File Explorer, mimicking the experience you get from the Share Charm located at the Charms bar. Installed apps that allow sharing will be able to work when you press this button, allowing you to experience the same share experience in Windows 8.1.
Here is what Microsoft's Brandon LeBlanc stated, in an official blog post today: "In the Windows 10 Technical Preview, we’ve added a new “Share” button in File Explorer to make it easy to share one or more selected files. Most file management happens through File Explorer, and now sharing is streamlined right where you need it."
Now when you have a few photos you would like to share to Facebook or Twitter, simply select these photos within File Explorer and tap or press the Share button. All done! This feature is currently in its early stages so expect more improvements and refinements as the operating system matures via consumer feedback.
If you are running Windows 10 Technical Preview right now, give this feature a test drive!