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 had a scare when i went to setup 2fa, I guess i only copied the last digits of the link thinking all I needed were the numbers and then I couldnt sign in, luckily I still had an open tab with my account signed in and was able to redo the 2fa before being completely signed out, with no email on the account I would have had to start over