You will need to complete the application form and submit it at the Visa Application Center for Greece in Nepal - Kathmandu. For the location click here
Under the new visa system implemented by all Schengen missions in Nepal as of November 2, 2015, all VIS visa applicants must submit their application in person in order for their biometric data (10 fingerprints and digital photo) to be taken. Please note that appearance in person for all applicants regardless of age is mandatory for biometrics.
Visa applications should be lodged no later than 20 calendar days prior to departure. Applications may be submitted at the earliest six (6) months before departure.
For further details, please consult the following notice from the Embassy of Greece: Notice from the Embassy of Greece.