Firstly download the app called "SonicWall Mobile Connect" from the MacOS App Store. The one shown below is the correct version.
Then download another app from the MacOS App Store. This one is called "Microsoft Remote Desktop 10".
Launch the SonicWall app you have just downloaded and click the Add Connection drop down.
Enter the following details (You may need to click the blue button for the rest of the fields to appear):
Name: Durrington High School
Username: Your campus username
Password: Your campus password
SonicWall may now ask you to add a VPN configuration. Select "Allow".
Now open the Microsoft Remote Desktop App. Click "Add Desktop" and enter the details:
PC Name: 172.22.16.20. Then click save.
To access this remote desktop you will need to open the SonicWall app and click "Connect". The remote desktop will not connect without you connecting to SonicWall. Once you are finished with your remote session click "Disconnect".
The remote desktop may ask you for a username and password. Your username will be "DURRING\YOURUSERNAME" and your password will be your campus password.