Unfortunately there is no ability to add audio within Google Slides.
However, all Chesapeake students are eligible to get Office365 for free. You can find the link by logging into MyCampus, and selecting "Help" in the green navigation bar, then select "Campus Help." Log in using your skipjack email and the site will guide you through the process. You can get access to the web version and the desktop version (if your device can support it). Once you log into Office365, on the home page, it will say “Install Office” on the top right, and you can access that link to download the desktop version of Office.