They work by giving you a random email address that is available for a short time (ex. 10min) and an inbox for any messages you recieve during that time (ex. an email verification message from a Lemmy server)
I didn’t want to recommend a specific one, however Googling “temporary email” should give you several options to choose from.
Another option: Gmail supports the “+” operator. If your email address is: Alice@gmail.com
You can use an email like Alice+eBay@gmail.com
To sign up for eBay. Now you can filter all of the garbage sent to that address easily! Bonus, you get to see who’s selling your data which is always frustrating and entertaining.