Let's say you have an 8-bar phrase to play. There are no chord symbols yet so you don't know what chords you'll be playing. You just have 8-bars in front of you. The first thing you need to know is the time signature. For our purposes here, we'll keep it simple and use 3/4 or 4/4 time.

Now let's select 4/4 time for our 8-bar phrase. Now we know the meter but what about the chords? Here's where we can jot down chord progressions for either improvisation or composition. For example, you may want to begin something in the Key of F Major. Having made that decision, you know that you have 6 chords to use right away. These are F Major, G minor, A minor. B flat Major, C 7, and D minor.

All that's left to do now is begin your piece in the Key of F Major. We usually start with the F Major chord itself so you now know that your first bar or 2 will be the F Major chord. But now a problem arises - how do you fill up the rest of the space? By using an 8-bar phrase to begin with, you don't have to worry about filling up a lot of space and taking forever to complete a section of music.

For instance, let's suppose we want to chart out an 8-bar phrase for improvisation purposes. We know what chords we will be working with. Now it's just a matter of fooling around on the piano and playing with the chord choices. You may want to place a chord change at every 2-measures. You can even use 2 chords for the entire 8-bar phrase such as F Major and B flat Major.

The whole point of the piano chord charts is to have a tool that will help you navigate what chords to play and when to change chords.