Major and minor: It's All Relative.

If you have access to a circle of fifths you may have noticed how the key signatures are ordered and paired.

On the outer edge of the circle you have the names of the Major scales associated with the illustrated key signature. Did you notice that another key signature, a minor key signature, is indicated in one of the inner layers?
We call that minor scale the relative minor scale of the Major key. You will probably see why the two scales are related based on this image...

The scales use the same notes but simply start and end on different notes. That's all it takes to transform the sound of the scale. It moves the order of W and H steps just enough to make a big difference.

When composing in a Major or minor tonality, you need to be aware of the differences in these scales and choose notes accordingly. Composing a minor piece that focuses on the notes C, E, and G will thwart the minor sound as the listener will hear a Major tonality. A melody in the key of a minor will probably highlight notes such as A, C, E to help establish the minor tonality.

Try it yourself...

Take a moment to compose a simple 8-measure melody in one of the relative minor keys. 

Your melody will use the key signature of the relative Major scale, but will highlight the minor sound.

8-Measure minor melody