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.
I’ve also seen people use temporary emails, forget the password or just need some sort of comms and then lose their account forever to the dustbin of time. These things happen.