I am placing a popup in my website. When someone signs up, I would like to send their information to Constant Contact and I would like the customer to be redirected to another page of my website. I did conact Constant Contact, they asked me to get API key. I am not sure what it is for and I dont know what to enter in their Application registration. All I want is a code to implement in my popup, so the customer information will be sent to Constant Contact database (Email List) and the customer will be redirected to one of a page in my website.
In your case where you need an embeddable form the answer is more difficult than having a simple form to paste. We are currently in the planning stages of designing a new system for embeddable signup forms, but we do not have a specific timeline yet for when we expect them to be available. Until this feature is complete, the alternative option is to use our API in conjunction with one of our API SDKs to create a custom signup form that is hosted on your website.
This option does require at least a small skill level in programming, as there will be some customization of code required to get the form functioning. If you have access to someone who can do this, or you are able to do this yourself, you can find our SDKs, which include samples for how to sign up a contact, here: http://developer.constantcontact.com/libraries/libraries.html
If you have any questions or concerns about this process, please let me know!