My partner had already recorded some guitar backing tracks. Like a chord sequence, or sequence of rifss, etc He played them out in a song structure, and sent me a rough mix as a computer file.
I then wrote lyrics/melody to match the chord sequences, and recorded several versions of them, including lead vocals & backing vocals, and sent them back as a computer file.
I also told him if he need to rearrange the order of the bits, e.g.
If the original sequences of riffs was say
I might have said, I need you to make
22114355 - where 55 was a requested new bit, or something
Or something like that.
So you see how 1 became 11, what I did was record two versions of me singing that bit, one version has the words for the first 1, one has the words for the second 1
So then we had to chop up and re-arrange the bits of the song to match the order of my lyrics / recorded vocals, send them back and forth.
Until we got the finished structure of the song.
Then we did vocal and guitar over-dubs using the same technique.
Then we did rough mixes, and final mixes, against sending them back and forth.
And then we kept doing it. Eventually we got about 18 songs, some of which have two or three different mixes.