These instructions are for using the Perforce Defect Tracking Gateway (Perforce Jobs Integration), which allows you to view FogBugz cases in Perforce (view instructions for using Perforce Trigger Scripts).
To submit changes to a FogBugz case, simply apply a job fix to the changelist for the corresponding job.
You can do this from the command line by typing (where job000021 is the job that corresponds to your case)
p4 fix -c 324 job000021
Or from one of Perforce's graphical tools by finding the option to add a job fix to a changelist and simply selecting the job(s) from a list:
Note that you'll probably want to Filter the results to find the case that you want. Here are some useful filters for finding your cases:
You can use these filters from the command line or from the graphical tools.