How to get the audio into your software
There are two common routes. The first is application or browser audio capture: many streaming and recording programs can capture the sound of a single window, tab or application as its own source. Add the browser that runs the soundboard and you can set its level separately from your voice.
The second is a virtual audio device. Install a loopback or virtual cable driver, set your browser's output to it, then pick the same device as an input in your broadcast or meeting software. Mix it with your microphone there. Exact menu names differ by program and operating system, so check your software's audio documentation.
Hotkey tips
Hotkeys on this page only work while the soundboard tab is in focus, because browsers do not allow a page to listen to keys in the background. A practical fix is to keep the soundboard in its own window on a second screen, or to put the board in full screen on a spare monitor. Do not type into the search box while hotkeys are needed: letters typed there do not trigger sounds.
Copyright on air
The built-in sounds are original synthesis under CC0, so you do not need permission and no one else owns them. Automated claim systems can still make mistakes with short sounds; if that ever happens, the sound licence page explains where they come from. For clips you own, use your own board, which keeps your files on your device.
Set levels before you go live
Sound effects are much louder than speech. Lower the master volume slider, test the air horn and applause, and watch your meters so a button never clips or startles viewers. "Stop all" or Space cuts every sound immediately.