You mean improvisation. You mean to sing on spot.
You mean to have only chords as a base and to come up with new melodies, riffs and runs and all the good stuff just on the go.
There are ways to train that.
There is one way, the simple and easy one to train a so called improvisation, to make it look like an improvisation.
And you need to be aware of these two styles and types of improvisation.
And it is all across music. When you are listening to a song and there is a guitar solo for example, and you get the impression that WOW he is playing that on top of his head and he is just improvising.
Most of the time he´s not.
Most of the time he has practiced and trained the chords and the chords progressions especially to know where the song is going, and what notes he can play, and what not, what sounds good and what doesn´t.
He did play around before he got on stage.
So most musicians and singers as well do this type of improvisation.
And there is the true and real improvisation that is really from the top of the head.
Where you come on stage and you just listen to the solo part for example (it does not have to be the solo part per se).
You can improvise anywhere.
It can be a fixed song already, and you can know what fixed notes you are going to sing but in the mood of the song, in the mood being on stage (you have a different mood than in the practicing room, right, in the rehearsal room).
Coming from this mood that you have you can totally improvise on top of the fixed notes that you are planning to sing something else.
And this will be real and true improvisation.
And you can also improvise in a real solo section wether you are a singer or an instrumentalist.
And you will be choosing those improvisations not necessarily from nothing, but you will have like a pool of little phrases, notes and riffs and runs that you have trained so many times that you will know, you will feel and know, what kind of little riff and run, and phrase, and little melody will fit into this chord that you are about to hear.
And you can train this (my phone is dying).
You can train this just by trying. For this, you need to train your ears very well because you need clean pitch to be able to improvise.
And you need to have a really good feeling for timing.
So pitch and timing need to be spot on if you want to be able to improvise. And you also need to train your ears to recognize harmonies, and to feel, to know what notes fit into the harmonies that you are listening to, that you are hearing.
And next step would be to just try.
And even if you sing the most horrible things, keep doing!
Only if you try you will get better.
If you don´t try you will never go anywhere.
So this is what I recommend.