You need to apply for a Schengen visa in person at the German embassy/consulate in your home country or a neighbouring country (if there is no German embassy or consulate in your home country) or the country where you reside. You can find the addresses of all German embassies and consulates on the website of the German Foreign Office. You have to make an appointment in advance to submit the application.
You can usually download and print out the form for the visa application on the website of the embassy/consulate. There you will also find a list of all the documents that you have to submit. If you cannot print out the form yourself, you can find it in your language free of charge on-site and fill it out.
Alternatively, you can fill out the form online at videx.diplo.de and then print it out. The website works in many languages.