There are many ways to make or find audio for your animation. You can record with your phone or other recording device, download music and sound effects from the Internet and extract audio from videos using an MP3 converter.
I highly recommend that you use copyright free material to avoid having your work blocked once it is hosted on the web. The Free Music Archive is a great source.
Test your animation by exporting to video and preview (see below).
To insert audio in your timeline, click the music note icon next to “Add Track” and add your MP3 file. Click the icon to add “new audio track” too.
To export your video, go to “File” –> “Export” –> “Render Video…” with the following setting (title it FirstName_LastName_Sample.mp4):
Credit your animation with this or something similar:
Produced by ____
Foundations of Art Design and Digital Culture
Penn Fine Arts
2019
Design of credits and audio on theses project work well with animation:

For final submission (before October 29 screening) post your rendered video (MP4) to the Project 2 – final animations folder on the Course Folder.
Resources for working with audio:
UbuWeb Sound (spoken word audios)
Convert Youtube to MP3 (audio) files (might have some ads – make sure you close spam tabs or have ad block on)
Epidemic sound (for 99 cents per sound)
You can use Adobe Audition to edit audio then bring it into the Photoshop Timeline.
In Audition, highlight the section you want, right click and select Copy to New, then save that and import it into Photoshop.
Here is a tutorial on how to work with audio in Photoshop
Adding Sound to the Video Timeline