Apostille is a form of official confirmation of documents for the proper recognition of their legal force in all countries that have acceded to the Hague Convention of October 5, 1961.
There is no single agency that would put an apostille stamp on a document. The places of application depend on where the document itself was issued and what you want to certify – the original or a copy.
Below you can download a sample application for an apostille in pdf format:
Antrag auf Erteilung der Apostille bzw. Legalization