The repeated command is added to the front of the command history unless it is identical to the most recently executed command already there. Even if you don't understand Lisp syntax, it will probably be obvious which command is displayed for repetition. If you do not change the text, it will repeat exactly as before. After finding the desired previous command, you can edit its expression as usual and then resubmit it by typing RET as usual. Each element is a Lisp expression which describes one command and its arguments.
Lisp programs can reexecute a command by calling eval with the command-history element.