Thank you for reaching out to Constant Contact API Developer Support.
It sounds like you might be trying to connect a 3rd-party app to your account and it is asking you for an API Key and access token.
Usually an application developer will generate their own API Key that lets their app communicate with Constant Contact, however some developers require you to provide them with your own API Key and/or Access Token. Since this process was designed for integration developers, it can be confusing for non-developers to find or generate this information. To help de-mystify the process for everyone, we have a blog post which walks through step-by-step instructions on how to get that information.