Sam wasn't giving you explicit directions like that because she really can't give those to anyone. There just isn't one basic way to masturbate.
Masturbation is about touching ourselves -- often including our genitals, but sometimes not -- in ways that feel good to us; about exploring ways we can be sexual alone through touching ourselves, whether that's with hands, toys or other objects.
To find out what feels good to you, you really just need to spend some time, over time -- over years, not just hours or days, basically for the whole of your life -- exploring your own body by yourself freely while you are also having sexual feelings or desires. We all find out what we like and don't, and what we do most because we found out a way to touch ourselves we like, just by trial and error, just like we find out what we like to eat and how we enjoy certain things served.
You know you're "done" at any given time when you feel done, when you don't want to do it anymore. Or, when you have to be done because there are other things you need to do.