Classroom is installed on all teacher's iPads. If you need Classroom on a different iPad please send an email to ithelpdesk.
The student iPads do not need the app installed.
Before you ask the students to connect to your classroom please make sure that all the iPads, including the one that you use, are on the same network (ISB), and that the Bluetooth is on. The devices need to be near each other for this step, 1-2 meters.
To learn how to set up a class (0.14), how to invite and add students (1.05), how to use the options, check on, and manage the students' iPads (3.15), please watch the underneath 8-minute video.