[sicksteve]

can someone briefly explain me what means to be in key? that means like the bassline to fit in with the chord? how can we tell? Noob question. But i have a guess: they must be in the same scale? and begin with the same note? srry for this question

[Evelon]

Like playing golf. You don't bring a hockey stick instead, just because they look a bit the same.
Yes, notes in a certain scale. Stick to them, until you know how to transit/change/break the rules.

[Glazed Ham Sandwich please?]

find a beginners guide to music theory.
read it.