Get started with Boot Camp Assistant on Mac
You can use Boot Camp Assistant to install Windows 10 on your Intel-based Mac.
Install Windows on your Mac
Depending on the model of your Mac, you might need an external USB drive to install Windows (you’re asked for one when you prepare your Mac for Windows if it’s required). Newer Mac models—with OS X 10.11 or later—use the internal drive to temporarily store the items you need to install Windows and don’t require a USB drive. To find out whether you need an external USB drive, see the “Learn more” section in the Apple Support article Install Windows 10 on your Mac with Boot Camp Assistant.
To install Windows on your Mac, do one of the following:
If your Mac doesn’t require an external USB drive: Follow the instructions in Install Windows on your newer Mac using Boot Camp.
If your Mac requires an external USB drive: Follow the instructions in Install Windows on your older Mac using Boot Camp.
Set the default operating system from macOS
After installing Windows, you can set the default operating system to either macOS or Windows. The default operating system is the one you want to use when you turn on or restart your Mac.
In macOS, choose Apple menu
> System Settings, click General 
in the sidebar, then click Startup Disk on the right. (You may need to scroll down.)Click the startup disk that has the default operating system you want to use.
Click Use Password, enter an administrator name and password, then click Unlock (or use Touch ID).
If you want to start up using the default operating system now, click Restart.
The next time you turn on or restart your Mac, it starts up using the default operating system.