If you want to find some Sound Effects (a bird song, a baby crying, a police siren or whatever), you can always try https://freesound.org/browse/
These are free to use - Freesound is a collaborative database of Creative Commons Licensed sounds. Browse, download and share sounds. You need to register to download.
Some are better than others, but you can audition them in your browser!
I am sure there are other free sound libraries people can recommend!