For your visa application, you need an application form. Fill out the form and submit it with the required documents to the competent German Embassy.
The suitable application form can be found here:
Application form for a national visa (German-English; PDF)
Application form for a national visa (German-Spanish; PDF)
Application form for a national visa (German-French; PDF)
Application form for a national visa (German-Chinese; PDF)
Application form for a national visa (German-Arabic; PDF)
Application form for a national visa (German-Turkish; PDF)
Application form for a national visa (German-Russian; PDF)
Application form for a national visa (German-Portuguese; PDF)