Settings > General > About > Version and there you will find a number similar to (4.2.1) or any other
Then here are several methods of obtaining the springboard and Cydia (click more):
DIRECTLY FROM YOUR IPOD USING JAILBRAKME:
If your iPod is Version 4.0.1 or LESS you can jailbreak your iPod directly accessing the web http://www.jailbreakme.com/ and CAREFULLY following directions. This is the easiest fastest way of jail breaking your iPod.
The second solution we offer is using the redsn0w program. To jailbreak your iPod with this program you will need a computer. Although this jailbreak supports all versions, it is much more complicated and we do not recommend it if you do not have a reactively high technology knowledge. If you want to here is a complete tutorial on how to use it: http://www.idownloadblog.com/redsn0w/
Once using this program you identify the version you need of it please search for where to download it in google.
USING LIME RA1N:
This third solution offers an alternative program, simpler to redsn0w but sometimes less effective. We highly recommend it as it is easy to use. You can find all the information related to how to use it in this web: http://www.idownloadblog.com/2010/10/09/tutorial-jailbreak-iphone-limera1n/
Remember to always ensure you are correctly carrying out the instructions in the pages given, we wouldn't want your iPod to be damaged accidentally and if it does remember it is NOT our fault, you do it at your own risk, even if it does (highly improbable) we would be very happy to give you counsel.