An auto responder campaign is one of six campaign types and is used to send a one-time email to contacts after they subscribe to your list. You can use this campaign type to send a "Welcome" message to contacts as soon as they subscribe to your list, or use it to send a "Check in" message a certain number of days/hours after contacts subscribe to your list.
A lead magnet (a.k.a. an optin bribe) is something amazing that you give away for free in exchange for an email address. This doesn’t have to cost you anything to create; most lead magnets are digital materials like PDFs, MP3 audio files, or videos that you can create yourself at minimal or no cost. It can be absolutely anything you want, so long as it provides value to your visitors for free.