I sometimes use sound effects with my English Language Learner classes as a game (playing sounds, let’s say, of animals and having groups having to identify its name) or as story-writing prompts (play some sounds in sequence and have students write parts of a related story).
Generally, I find Free Sound as the easiest place to find them, but I have lots of others sites at The Best Places To Get Royalty-Free Music & Sound Effects.
Here are some posts other ELL (and non-ELL) teachers have written about how they’ve used sound effects with their students:
Teaching With Sound Effects by Hall Houston.
The Sound Book by Mike Harrison.
Using sound in the classroom is from Learn NC.
ESL Halloween Lesson Plan – Scary video and sounds
Here’s an animal sound quiz.