I quite don’t understand your question here but I can try to help you 
When you register an app on apps.twitter.com, what you actually do is to register an application in order to get access to API. You can then interact with the Twitter API through the credential you have when you click on your application under the tabs Key and Access Token.
You must provide the API Key and API Secret in order to configure access to Twitter.
You can find all details about how to use the API here https://dev.twitter.com/web/overview and here https://dev.twitter.com/twitterkit/overview depends on your need.
Your app will be visible by user when they login through your app in order to authorize access to their account.
I hope the response helped you
Let us know if you need more details about how to implement twitter inside your app, it will be a pleasure to help you through the process ^^