I would really like to understand this - I really, really would!
The trouble is that merely expressing these ideas in words gives no idea about what the notes/intervals actually sound like. And telling me about notes on a piano doesn't help either as (a) I haven't got a piano and (b)I would have absolutely no idea which keys to press if I had. I also suspect that playing scales (on some musical instrument or other) would be of limited use because I would struggle to hear how they would relate to actual tunes which use that particular scale/mode.

Is there any way into this for a musical ignoramus like me ... ?