This function silences the selected region. This function can be useful to remove breaths or clicks from a voice recording without changing the timing of the words.
The menu item Edit -> Insert Silence is used to insert silence of a specified duration at or over the selected location.
The Trim Silences function can be used to remove or shorten silent regions. For more info, see Trim Silences section of Trim.
Any part of your audio which is below a certain threshold will be attenuated by the amount you specify. For more info, see Noise Gates section of Noise Reduction.