Packers are different for every guy out there.
1, to show you have a bulge in the groin area.(if you want one that is)
2, to stand and pee in a male toilet. (again if you want to do that)
3, to have be able to have sex. (I'm not sure if your old enough just yet)
Also I do believe that on you-tube, there are guys who show how to use them.
There are many sites out there who sell packers, it's up to you.
If you go into the FTM section here there will be sites that you can look up.
