Hl sir ... i am manisha from nepal, how to apply for Hong Kong visa

Manisha, you should get a passport first. You can apply for a visit entry permit.
If your sister be your sponsor, the required documents include the application form, a recently-taken bareheaded color photo, copy of your passport, relationship certificate between your sister and you (household registration, birth certificate or family photographs), your financial support proof, flight itinerary, the application form filled by your sister, copy of her passport and HK ID Card. And then ask your sister to submit the application to HK immigration department to apply.