The initial Soundmoji library includes sound cues for standard emoji including applause and a drumroll as well as evil laughter. There are also audio clips from artists such as Rebecca Black (it's hard to imagine would be most appropriate for that Soundmoji) and movies and TV shows including F9, Brooklyn Nine-Nine and Bridgerton. Facebook will add more sound effects and clips over time.
If you really want to risk the wrath of your friends and family by bugging them with Soundmojis, open a Messenger chat, then tap the smiley face followed by the loudspeaker icon. You'll be able to preview Soundmojis from the library before sending them. I wonder what an eyeroll sounds like.