Just like the technical material allows you to physically support your development as a singer by allowing for greater flexibility (which helps range), strength and co-ordination, generally speaking people want to develop those things in order to freely express themselves musically. So it makes sense to include some musical material in your practice aside from specific songs and it’s also fun.
These improvisation tracks just go between two chords, which allows you to really explore what possibilities exist there. At the start, there’s a lovely tasteful synth that plays a melody, which you can either use as inspiration to sing back, or you can respond in a different way.
To begin with, just see where your ear wants to go. Don’t worry if you sing some dissonant notes. That’s all part of the process of your mind/ear mapping what’s consonant with the chord and what isn’t. Doing this type of thing starts to cultivate and develop your own sense of melody and expressiveness. Use these tracks after you’ve done the physical warm up and use them as creative stimulus.