A chord progression is a series of chords laid out in time. Which chord you start from, where you move, and where you settle create the mood and the development of a song. Even with the same melody, changing the chord progression changes the impression greatly.
The flow a progression creates
Holding a single chord keeps a song in one mood. Moving to another chord creates motion, such as expectation, tension, and resolution. A chord progression is the foundation for designing the emotional path of a song.
Working within the key
In most songs you choose chords based on the key and the scale. In C major, for instance, C, Dm, Em, F, G, and Am are the basic candidates. The chords that connect naturally within a key like this are called diatonic chords.
A common way to start
Around four bars is easy to handle at first, lining up four chords such as C→G→Am→F. Play each chord for one bar and try a melody or a rhythm over it. Repeating a flow you like and swapping just one chord in the second half is already development.
Programming it in a DAW
Decide the key of the project and place the chords one bar at a time in the piano roll. In DAWs with a chord track, you can enter the progression first and then build the accompaniment and the bass. If you use loops, check that the key written on the material fits the progression.
Theory widens your options
You can use a standard progression as it is, or change a chord partway through. Start by making a flow where your ear says it wants to go somewhere next, or that it settles here, and confirm the reason with theory afterwards.
