The image below is of the background on the middle 3D computer station. You will see it has an image of each machine this computer is able to print to and corresponding instructions underneath. As this is the background image to the screen these instructions will always be available to you. The RED boxes on the image indicate clickable links to tutorials to give you a better understanding of each of the software meant to operate its corresponding 3D printer.
For Ultimaker 3D printer you will need to double-click the "Cura" icon to start the Cura software.
Once the Cura window opens you can load your model in two different ways. As seen below, if you have your .stl on the desktop or in a File Manager window you can click and drag the file into the 3D plane. Otherwise, you can go to File -> Load Model File and select your .stl.
After your model has loaded into the 3D plane, the icons for Rotation, Scaling and Mirroring will appear.
When you are ready to print you can do two methods to achieve this. One method is to click the "Print with USB" icon in the upper right of the 3D plane window or you can go to File -> Print. After selecting this you will have a "Printing on COM206" dialog window and when the "Print" becomes highlighted, click it, and your print will begin.
Please be mindful of the time your model needs to print.Time to complete should be before the library closes.