My girlfriend is in HK she want me to come to HK and i want the same how can i come and live with her there ? please guide me .

Suhrab, you can apply for a HK tourist visa for that, but it may not allow you to stay for a long time.
First, you need to prepare the required materials including copy of passport, an invitation letter from your girlfriend, a fully completed application form, a recently-taken passport-style photo, financial support proof, and flight itinerary.
Next, submit the application to Chinese embassy in Afghanistan to apply for HK tourist visa.