How can I safely jailbreak my itouch 3g running ios 4.1.2?

I have never jailbroken before, and I am confused about how I am to go about doing it. I haven't found anything on the internet that can answer my question simply and straightforward. I have an ipod touch 3rd generation running ios 4.1.2. Also, I want to make sure that my ipod is safe and that there is a way to get rid of the software in case I need to go to Apple.