As of July 1, 2019, Back to My Mac service is no longer available. You can use these alternatives for file access, screen sharing, and remote desktop access.
Access files across your devices with iCloud Drive
When you turn on iCloud Drive, your files automatically upload to iCloud, where they're safely stored and available on all of your devices. Turn on the Desktop & Documents Folders option in iCloud Drive to store them in iCloud, too. Now you have access to all of your files, on all devices, at any time.
You start with 5GB of free iCloud storage and can upgrade any time from any device. iCloud Drive has an individual file-size limit of 50GB.
Access your other Mac with screen sharing
If you have more than one Mac, screen sharing lets you use one Mac to view and control your other Mac on the same network. This means you can open, move, and close files and windows, and use apps from another Mac. Learn how to set up and use screen sharing.
Manage your Mac deployment remotely with Apple Remote Desktop
If you want additional remote management capabilities, such as installing and configuring apps, helping remote users, and creating detailed reports, you can buy Apple Remote Desktop from the App Store. You can use Remote Desktop to remotely manage Mac computers in a commercial or business environment. Learn how to use Remote Desktop.