Once you know a particular scale, it is not enough just to learn it and be able to play it through. You also need to make an effort to become familiar with the various chords within the scale. Each song in the minor key will use these chords in a particular chord progression. The chord progression itself will involve at least two chords. To use such progressions effectively, you must find out what is available in terms of that scale.
A little thought will show that because the A minor scale uses the same notes as the C major scale, both keys share the same chords. And so they do. The difference between them is how they are used (see Table 9.1).