We create the certificate either as a PFX file suitable for windows or as text files (.crt) suitable for *nix and many other systems.
The only requirement is that you can receive an email at one of the following addresses
admin@ administrator@ hostmaster@ postmaster@ webmaster@
To install the certificate in windows you just need to double click on the pfx file.
For *unix and many other systems where you usually have some kind of control panel, you usually paste the text in the files into a form.