Extensions in iOS 8 make it easier for apps to talk to each other. More precisely, they allow you to send information and data from one app to the other or use an app from within another app. Extensions are essentially apps themselves that need to be enabled from within share menus for them to work. They work with as both share/action buttons and as stand alone apps. Here’s a quick overview of iOS extensions and how to enable them.
Not all apps have an extension and not all extensions work as stand alone apps. ViewExif is an excellent example of an extension that works inside the Photos app. To enable an extension, open any screen that might have a share button like the Photos apps. Tap it and swipe till the very end of the share options.
There are two rows of actions that you will see; the top row is reserved for actions that will send data from the current app to another one. For example, if you’re viewing a picture in the Photos app and want to open it in Evernote, it will appear in the top row.
The bottom row is reserved for in-app extensions such ViewExif mentioned above. These extensions will work entirely from within the current app. Some extensions, like Quik Downloader work as an extension and also have an app interface.
Tap the more button at the end of a row, and you will see a list of ‘Activities’ where all app extensions will be listed. The default ones cannot be turned off but when you install a new one, you will have to turn it on from a share screen. The activities can be dragged and dropped one over the other to reorder them.