To backup your files with OneDrive, you'll need to turn on the feature in the "Backup" tab of your OneDrive settings.

When accessing your files, File Explorer is your go-to option. When you click on File Explorer, it opens up a default view that gives you access to the default folders, like desktop and pictures, ...

You can share files and folders on OneDrive from within Office apps, from your desktop, or from the OneDrive website.