The 3i Spinning Disk Confocal is equipped with a variety of stage inserts to fit a myriad of sample vessels. The insert fitted onto the stage when you start up would be what the previous user was using, and you may find that you'll have to change it. The inserts are usually located to the left of the microscope, inside the chamber.
There are two inserts, both with ASI Imaging written on them, which fit directly onto the stage. These are a multi-well plate holder, and a universal K-type holder. Neither of this are connected to the CO2 supply. 
The CO2 chamber also sits directly on the stage (make sure there isn't already an insert fitted). The CO2 chamber takes the 3 OKO lab inserts for 35mm dishes, slides & labtech chambered coverslips. 
Each of these inserts have small magnetic clips which are usually in the takeaway box near the wall. These clips are for holding samples firmly if you wish to use them.
If you wish to do multiwell imaging without CO2, you can use the CO2 chamber without any inserts.