Ok, if you have two hands, raise your picking hand high up sky. Good. You see the side with no thumb attatched ? THAT's your palm muting side ! Great, now we have found an essential part to palm mute: The side of you hand. Ok, but what to do with this so called 'side of my hand' ? Good thing to ask ! You have probably got a guitar right ? Well, you see the thing were the snares come out of (=bridge) ? Don't lay your 'side of you hand' on the bridge itself, but a little after it so your 'side of your hand' is resting on the snares. Now, since this is your picking hand it should contain a pick (or fingers). Found it ? Now pick any note and you have a 'Palm Muted' note.
Everything you learn asks a bit of practise, so don't think you're doing it wrong because it doesn't go smoothly. Just read the explenation a couple times and do some exercises (powerchords muted, simple chromatics, etc.). I remember when I first learned to palm mute, it felt really strange, but after a while I got used to it and it began to come smoothly.

Hope I helped you :)

Latz, Gulder