Hi Dayzd,
I’d be happy to answer your question!
Most western music is written diatonically. This means that all the notes in the song, are part of a scale.
A chord is a group of notes, stacked in thirds. For example, C E G is a C major chord. There are 7 notes in any diatonic scale. In the case of C major it’s, C D E F G A B. Because there’s 7 notes, we can make 7 chords: C major, D minor, E minor, F major, G major, A minor, and B diminished.
In music theory, we assign each one of these chords a number (in roman numerals) based on their position in the scale.
Go to: http://www.hooktheory.com/theorytab
There you can see all this in action.
HookTheory also has a song editor here where you can make your own songs.
I HIGHLY recommend it if your interested in song making.
To answer your question:
You can really use any chord that sounds good to you.
Traditionally, there are also rules that you can follow.
If you’d like to learn more about this, I’d suggest getting a book on harmonic theory specifically. The Musician’s Guide to Theory and Analysis (Second Edition) is a very good book for learning harmonic theory. You can find it on Amazon here.
Let me know if there’s anything else I can help you with.
I’d be happy to help.
Giovanni