If you wish to allow your audience to send in comments while holding your presentation so that you can get feedback throughout the session you can enable the Comments from audience feature.
The comments will display for a few seconds in the Presentation view before they disappear and will not be saved for exporting afterwards.
If you want your audience to send in questions that don't disappear and are available for export, you can use the Q&A feature instead.
How to enable Comments from audience
Open the "Settings" menu in the top right corner of the Edit view
Scroll down to "Comments from audience"
Toggle "Allow audience to give comments"
You can also toggle this feature on and off during your presentation by opening the presentation menu at the bottom left of the screen or simply by using the keyboard shortcut "E":