Setting up the Windows 10 Companion app - a guide

Setting up the companion app using the example of image synchronization

Type "companion" in the Windows 10 search bar at the bottom left.

Then open the "Companion for phone" app. Connect your smartphone to the computer and decide in the companion app, depending on which smartphone you have, for the Windows Phone, an Android smartphone or the iPhone.
In the next step you can save your data on your computer as a backup.
For example, to back up your photos on your Windows 10 system, click on the "Get Photo, ..." button "Get Started".
To automatically synchronize your data, you need to use the same Microsoft account on your PC and smartphone. Click "Yes, that's me!"
If you carry out the configuration with an iPhone, you will be asked to install iTunes. Then click Next".
Download the OneDrive app on your smartphone and log in there with your Microsoft account. Check the box next to "I am logged in to the OneDrive app on my iPhone" and click "Next".
You may now have to allow camera upload for the OneDrive app on your iPhone. Then tick the companion app that you have done so and click "Next". Finally click on "Done".
In the OneDrive app on your smartphone, you can now select the photos you want to sync.

When you start the companion app, you can not only synchronize your pictures, but also all other data.
After you have decided on the device type, there is also the option of synchronizing your notes, your Skype account, Office and your emails.
Do this in a similar way as explained in the first section. Depending on the data type, other programs may be necessary. The respective configuration wizard will instruct you.
You will soon be able to get Cortana on your smartphone at this point.