MFDs are located on the ground and first floors in Main Physics, and MSci students are not currently charged to use these devices - however use is recorded and suspected abuse will be investigated. Don't be the person who ruins things for everyone. The computers list mono and colour queues for staff and students - use whichever is appropriate.
In Fedora 28 there are issues with print authentication, which means things don't work as well as they should. In principle the computer should be able to use your QOL credentials from logging into the computer to talk to the print servers, but that is broken, and despite lodging a bug report in July it has not been fixed. This means you'll need to manually authenticate at times.
If you try to print from one of the GUI apps, like LibreOffice, or Firefox, you'll see a popup like this:
Enter the username as ads\studentno - replacing studentno with your student number. The password is your QOL password. Click the Remember Password check box; that should mean you won't have to do this again for that printer.
If you try to print from the command line, or some older applications, you will instead see a popup which advises that credentials are required:
Clicking on the alert will take you to the printers control panel, where you will see the list of jobs waiting for authentication.
Click on the blue Authenticate button and enter your username and password as above; note that this dialog does not offer to save your credentials, so you'll have to authenticate each time. If this gets tedious you may want to alter your workflow to print to PDF, and then use the PDF reader application to print.