#1
What are relative chords? Are they the chords falling under a particular scale or something? I tried searching the lessons section but found nothing. Help?
#2
It means you have the same key signature but different tonic. Take A minor and C major, for instance. Neither of them have no sharps or flats. Therefore, A minor is the relative minor of C major. You can find the relative minor's tonic by going down three semitones from the major's tonic.
#3
^^Adding to your thoughts, relative chords are like I of C Ionian (Cmaj chord), and III of A Aeolian (Cmaj chord). Two chords in relative modes, which have the same notes, but are on different degrees of the different modes (due to them having different tonics)