If you want to learn more on this topic, check out this lesson from the free version of my Beginners Course!
Pop songs are always in a ‘key’. This means they use certain chords that go together well, which are derived from corresponding the major scale. Music teachers always explain the key of C first as it has no nasty ‘sharps’ of ‘flats’.
These chords can be seen like colours that go together well- meaning any of these are a safe choice and a song in the key of C would mainly use these chords and few others, if any. As well as the chords, we can play notes from the C major scale (next page) over the top of these for the melody
Example chord sequences in the ‘Key Of C’