Hi Collins:

In very simple terms, the key -- or key signature, as it's called on the musical staff -- refers to which notes are played sharp or flat, if any, throughout a given tune or song.

When playing a scale, the key dictates which note you start and end on, as well as which notes you will play sharp or flat on the way up and down.

Any given tune/song can be played in pretty much any key (I won't get into modes, which is related but something to learn later on). Changing the key changes how high the highest note in the tune/song is and how low the lowest note is. Being able to play a tune in different keys is important if, for example, you will be backing up a singer. One particular key might fit the singer's vocal range better than another.

Here are a couple of good references for you:

http://en.wikipedia.org/wiki/C....._of_fifths

http://en.wikipedia.org/wiki/K.....28music%29

The concept of musical keys is way more complicated than my simple explanation, but those are the main points that you need to know, IMHO. I hope that helps. I'm sure others will weigh in with better explanations.

Welcome to the forum! -- Diane