Hellow Sir/ Madam, I am a Sri Lankan passport holder .

Harsh, if you want to visit all the 3 places, then you need to apply for 3 seperate entry permits. You need to submit the required materials to the embassy of PRC in your country. The three places require the same basic materials including the application form, your passport and its photocopy and your recent full-faced color photo. Other relevant materials are a little bit different.
For PRC: hotel reservations and joint-way air tickets, travel itinerary, a letter from the local travel agency or other travel organizer, “Invitation Letter for Tourist” from Chinese Tourist Bureau as well as financial support document
For Hong Kong: proof of your financial standing such as bank statements, savings accounts passbooks, tax receipts, and transportation arrangement such as flight itinerary, as well as travel plan to HK
For Macau: financial proof, round-trip air tickets and hotel booking records, as well as your travel itinerary