I'm very new to FreeBSD and programming. I don't understand how to create a txt to use the calendar utility to display notes 
Calendar to Cal displaying schedule
calendar;cal
To edit a text file, use whatever editor you have available, or install one.  nano, emacs, and vi are common ones.If the calendar utility we're talking about here is the command calendar as described here, then the format of the file is described by the manual.The file should be called .calendar (with a leading dot) and be placed in your home directory.