Yeah, my questions are getting tight ..... and so are my chances to fuck up the car

So I'm thinking to do this valve thing and I've been reading and searching quite a lot lately. My question is how do you determine that the valves need adjustments in the first place? Or "noisy" to quote the book. The car sounds fine and quite but there is this metallic sound that I hear mosly when the engine is cold. It's sounds like if you were to hold your of keys and shake'em. Alright, I know it's funny and kinda pathetic cause most of you know exactly what I 'm talking about but ... hey ..just in case.