pls let us know 1st time Hong Kong travellers visa requirement for sri lankan passport holders

Ranjan, you should apply for the HK entry permit through the embassy in advance. The aplication may take four to six weeks, so you need to plan your schedule well. Documents required for submission include:
Application form (ID 1003A)
Your recent photograph
Photocopy of your passport
Photocopy of proof of your financial standing and proof of employment (if any)
Photocopy of proof of transportation arrangement, e.g. flight itinerary
Photocopy of proof of the proposed leisure visit to HK, e.g. receipt of joining a package tour to Hong Kong, itinerary, etc.