Problem with Metasploit Ruby Language

I am not really familiar with ruby programming language neither a professional in metasploit, I really need to understand how this exploit ms01_033_idq.rb works.
what I don't get is target.ret[-4, 4] and rand_text_alphanumeric(1). I wonder if you could help me figure out what these commands are and what they actually do.

Thanks in advance

Here not is support for metasploit.

For more information, see.

Metasploit Unleashed - Mastering the Framework

And join the irc channel.

#metasploit

Regards,