There are a couple of ways...
1. You can use the audio action "set muted" to mute any sound on command and then have your mute button set all running sounds too muted.
2. You can have all sounds called from their own group and then set that group disabled on mute.
3. You can give the sounds you want muted audio tags for "muted" and "unmuted" with event actions that use "is not "muted"" in order for sound to be played.
4. Or as mentioned above you can set the master volume if you want everything muted.
I think the first one is the easiest to use unless you want to mute everything. It is the one I used for music mute option in Capt. Doe Saves the Universe.