You can see here how you can sign up in Engagement Builder.
Since Engagement Builder is built using Twitter OAuth v1 we need certain permission in order for the app to work. Those permissions are Read and Write.
The first permission will allow us to read your tweets and present them to you, see your audience, access your lists, etc.
The write permission allows us to send your tweets, replies and mentions, to Twitter and publish them for you.
If you decide not to grant us those permissions, unfortunately, we are unable to provide you with our service because it heavily depends on those permissions.
Once granted you’ll be redirected to our app and you’ll see quick onboarding info and you’ll be able to pick the most interesting topics for you. After that you can start using it immediately.