How can people opt in and opt out of my lists?

If you do not have your contacts database set up yet, you can place a Textmagic form on your website to gain more opt-ins. You can read more about these forms here.
You can also create an automation rule and ask people to opt-in by sending a keyword to your dedicated number. 

People can simply opt out from your communication by replying STOP, STOPP, STOPALL, UNSUBSCRIBE, END or QUIT to any of your messages. Once they have opted out, you cannot send messages to these contacts anymore.
If you have opted out by accident, please contact us and we will assist you further. 

Your customer can also send you an incoming message with these keywords to resubscribe: JOIN, SUBSCRIBE, RESUBSCRIBE, OPT IN, OPT-IN, OPTIN orUNSTOP.