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.
Yep, super convenient. I now use Fastmail where this is built in, but nevertheless, very handy.
Same here, signed up a couple of months ago and have made good use of it when trying out services.