Nepali and certain non-EU nationals need a visa in order to enter Germany. An Overview of visa requirements/exemptions for entry into the Federal Republic of Germany can be found here.
The type of visa you require depends on how long you plan to stay. Are you planning a short visit to Germany, e.g. for a holiday? Or would you like to stay longer, e.g. to attend university?
Please choose how long you are planning to stay.