At first, I improvise some songs with my accordion, or my piano.
This improvisation can take for hours before finding the right melody.
On the accordion, I can search the melody with the right hand, and the drums rhythms with the left hand, tapping on the bass buttons.
So it's easy to get a melody, harmony and drums rhythms for a whole song with just an accordion.
But while I'm playing the song, I must think the melody for different instruments...
How I proceed ?
Then, when I have all the music in my mind, I compose the song with Guitarpro.
Through my years of musical theory, I can easily write music scores (that's useful if I need real musicians to play the song).
So I introduce all the instruments I need, manage the volume (pianissimo, piano, mezzo forte, etc...), and all the other parameters of the score.
Now, music is not only in my mind but also in my computer.
But this is a .midi format (it's a lightweight format containing all the digital data : notes, tempo, etc...), and the quality of .midi songs is not good and that merits further work.
Finally, I rework the .midi song on a sequencer (Cubase).
I give more depth to the music and a much better sound quality through VST instruments, and using as much of the compressors, equalizers, reverbs, etc...
I sometimes add sound effects on percussion, or to create a different atmosphere to the music.
After hours and sometimes days of work, the song is finally over.
I usually export to .wav, .flac or .ogg format (which guarantee excellent sound quality).