Herb has you started off in the right direction and BIAB makes it REALLY easy to do what he just said, with Chord Builder. See attached screenshot. You get to it through "Edit" on the top of the menu. Or use Chord Builder icon at the near bottom right hand side of the screen, before the chord input bars start (just above User Tracks Icon).
This is all very simple, actually. Let me break it down.
1.) Yes, Herb is right. In Pop, country, whatever you basically have 4 chords--the I, IV, V, and VI minor.
In the Key of C, that would be C, F, G, Am.
2. There are approximately 24 "standard" chord progressions built from just these four.
For example, at one chord per measure in a fast song, the Verse chords could go:
C, F, G, C, or they could go C, F, C, G, or they go could C, F, C, F, or they could go Am, C, F, C
Here are some common examples:
[Chords]
|a) C| F| G| Am| C| F| Am| G|
| C| G| F| Am| C| G| Am| F|
| C| Am| F| G| C| Am| G| F C|
[ChordsEnd]
But at any rate, if you just "shuffle" your choices starting with the I, IV, V, or VI, you get at least 24 common variations--or more, depending on your variations. Try them all.
For slower songs, you would have 2 chords per measure, kinda sorta, but the concept is the same.
3. The non-fast but general "kinda sorta" rule is that you can't start the Verse and chorus on the same chord. This is not hard and fast, but the idea is, try to do something different in the chorus. If you start the verse on C in the Key of C, try starting on G in the chorus for a lift. If you started the verse on G in the Key of C, it might work well to start the chorus on C (the I). Try it.
4. Look at the Chord Builder. If you click on any chord you will heard it play and it will enter it for you. If you don't like that sound, pick another chord.
5. Once you do what Herb said and START the song by punching in some common standard version of a I, IV, V, VI minor you call THEN go to chord builder and look at all the chords on the top row that will work in that progression. Try them and see how they sound. The lower rows are for jazz. (But the slash chords are also critical for rock, folk and pop to build emotion. You must master them.)
So, Chord Builder makes it really easy to experiment. Really easy. Try it, use it, experiment. Have fun. That is what music is.
P.S. You also have to find your range before you put chord to a melody. For example, lots of baritones are most comfortable in the Keys Eb, E, F, G, Ab, A, Bb, B or C, in that order, where C contains the
highest notes you would hit.
If you were to write a song in the key of G where the highest notes are above middle C in the Key of G, then a baritone would not be able to hit those easily. That is, some baritones cannot sing a high melody in the key of G unless it is shifted down a whole octave, and that doesn't sound right.
If you write a melody in the key of G with high notes, and the Baritone says, I can't do that, try the Key of C with the melody transposed down. If it still does not work, try Bb.
Hope this makes sense.