I gather the technical information doesn’t help. A major chord has the bottom note, middle note and top note. The middle note is two steps above the bottom note. Confusingly, two steps is the interval to the “third.” That’s because it is the third note in the scale, if you start counting at the first note.
The top note is a fifth above the bottom note. It’s actually the fifth note in the scale, although it is only three and a half steps above the bottom note.
Each note has other names, too. The first note is called the “tonic.” The fifth note is called the “dominant.”
Anyway, each major chord and each minor chord has three notes. Two of those notes are the tonic and dominant. It doesn’t matter what key you are in, the relationship is always the same.
What changes is the third. In a major chord, you use the major third which is two steps above the tonic. In the minor chord, you use the minor third, which is one and a half steps above the tonic.
The sound of major and minor chords are dramatically different, and you probably feel it in your body even if you are not consciously aware of it. The major chord is happy feeling. The minor chord is sad. Major is bright and light. Minor is dark and melancholy.
Trust your feelings. Listen to the song and figure out the mood of the song. Most likely, if it’s a happy song, it will be in a predominantly major key, and if it is a sad song, it will be mostly in a minor key.