You can email the customers who asked to hear from you — and only those.
How people join your list: When someone books a table and leaves an email, they see a tick box: "Email me news and offers from this restaurant." If they tick it, they join. If they don't, they don't.
You cannot add anyone yourself, and that is deliberate. The email addresses already sitting on your bookings were given to you to answer that booking — not to receive offers. Using them for marketing is not something the customer agreed to, and no unsubscribe link makes it something they did.
This means your list starts empty and fills up over weeks. That is normal, and it is the point: everyone you eventually email actually asked for it, so your messages land in inboxes instead of spam folders.
Sending: Open Email campaigns, write a subject and a message, and send. An unsubscribe link is added to every message automatically — you don't have to write one, and you shouldn't try to remove it.
Unsubscribing: One click from the email and they're off, with no login and no "are you sure". If someone asks you in person instead, you can remove them from Your list.
People who unsubscribe stay on the page, greyed out. They are never emailed again, and booking their next table won't quietly put them back — only they can rejoin, by ticking the box again themselves.