That says quite a lot, and error messages like that are very valuable (otherwise they'd just be silent and say it crashed)
It reports that at line 13 there is a problem with the syntax. keyword_end refers to the
end keywords that you put after methods, loops, classes etc. And $end refers to end of file. With that you should be able to make sense out of that error message. Error messages are also usually very good search queries if you don't understand them, somebody else is likely to have asked about that same error message.
A somewhat newer ruby-version would phrase it this way instead:
14: syntax error, unexpected end-of-input, expecting keyword_end