How to Use The Send HTTP Post?

Someone explained to me that a sequence can be set up to achieve:
After the first email in the sequence you can set up, that once the contact has recieved the email that i can start a new Facebook campaign for that contact. then once the next email in that sequence is sent to that contact that it can remove them from the first Facebook campaign and add them into another one with same content as the email…Is this actually possible? If so, can someone talk me through it. I don’t understand how to make it happen, if its true. Thanks in advance.