The 3D printer in the Creator Space is an Ultimaker 2+ with a print size of 223 x 223 x 205 mm. You can use any number of CAD softwares to design creations to print, but probably the easiest place to start is with Tinkercad. It is free to create an account and all creations are saved automatically to the cloud. One account can be used for many creations at once, so a teacher can create one account for a whole class to use at the same time and then have access to all the creations. Once a design is created and ready, you can download it as a .stl file then prepare it for the printer using Cura.
Tinkercad had a bunch of great resources for getting started in their software. You can go to this link and follow along with a bunch of lessons on how to use the software.