When the program is run, you asked to enter the character you want to redefine. Here's the first snag. You can choose a normal ASCII character by pressing the appropriate character but to enter characters not directly available from the keyboard, you enter the ASCII code. This may sound reasonable if you could see what figures you're typing in. There's no cross-reference so you must look up the ASCII code in the user's manual.
The editing isn't very sophisticated either. You design your characters in the usual cursor-on-a-grid fashion but there are many short-comings. For a start, there is no wraparound and there are no useful facilities such as rotate, invert and clear. There is no facility for defining more than one character at a time either.
Perhaps the most frustrating part is that you cannot see your character in actual size as it is being edited and you are not given the necessary values for the redefined character. To top it all, you cannot save or load the redefined characters from within the program.