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.
please don’t use a temp email (or non existent) for anything you might care about. also, make sure you never typo your email address.
example:
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.