Abgeltungsteuer

Plus Soli and, if applicable, church tax. German banks withhold it automatically, which settles the tax in most cases.

With a foreign broker nothing is withheld, so you must declare the income in your tax return yourself. A tax-free saver's allowance applies if you file an exemption order (Freistellungsauftrag).

General information on German tax law, not advice on your individual case.