The form elements at the bottom of the Manage fields page let you add fields and groups to your content types.

(The Add existing field row is displayed only if there are fields available in other content types. The Add new group rows is displayed only if Fieldgroup module is enabled.)

Your fields and groups will be created after you click the Save button at the bottom of the page. In subsequent pages you will be presented with the settings form for each field you added.

You will find more details on the required informations in the following pages: