"Pop" if they are really young, "probe" if they are older. Like Nanci said you can google some youtube videos.
However, I would strongly recommend you do not do this yourself for the first time just by learning from a video, as it is possible you might accidentally injure your snake. If you just want your snake sexed, you can have a vet do it for you. If you want to learn how to sex CS, you could try to find a breeder or vet to teach you how to do it safety.
Also, if knowing absolutely is not important, there are visual way (totally safe) that you can do by observing the differences is where the tail tapers off between male and female CS.