The SkyDrive app has three screens: files, recent, and shared. The files screen shows all of your files, the recent screen shows files you've recently accessed, and the shared screen shows files and folder that have been shared with you by other users.
To open a file or folder, just tap on it. Files will be opened in the app associated with them--for example, Word documents will be opened in the Office app while pictures will be opened within the SkyDrive app.
At the bottom of each SkyDrive screen is the menu bar, which has four buttons: add, thumbnails, select, and search, along with the More ellipsis button to access additional features. The add button lets you add files to your SkyDrive (including to different folders in your SkyDrive). The thumbnails button lets you toggle between viewing files as thumbnails (the default view) or as a list with extra details such as name, size, and date created. The select button lets you select one or more files to move or delete; the search button searches within SkyDrive for your media.
The More ellipsis on the menu bar lets you access more features, including the ability to add new folders, refresh your SkyDrive, and access the settings panel. You can rename any folder in your SkyDrive by tapping on it to open it, tapping the ellipsis, and tapping "rename." In the settings panel, you can see how much space your SkyDrive has available (in the account pane), and you can choose photo upload and download size (original or resized) in the general pane.
Once you've opened a folder in SkyDrive the menu bar changes slightly to provide you with different features--most notably, the 'thumbnails' button changes its name to 'details' when you've organized your folders in list form, and the 'search' button is replaced by a 'share' button that lets you share files using an email link. You can also share folders by copying a link to the clipboard, or by tapping the 'permissions' button and adding contacts or email addresses to the folder.
While the SkyDrive app isn't necessary to perform simple backups, as Windows Phone 8 has those services well integrated, it is worth having if you want to be able to manage your SkyDrive files and folders on the go.
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