Mix a noise with a signal

Sorry for the dumb question, but it’s just stuck in my brain. - I mark a signal in a track and generate pink or white noise. Either they mix together (signal and noise), or the noise just substitute of the signal?

If you select part of an audio track and use any of the generators, the generated sound will replace the selection.
If you want both the original sound and the generated sound, add a new track (Tracks menu) and make the selection in the new track.

Thanks! A am free!!!