Hi, i am a vietnamese and would like to visit hong kong and macau. What visa do we need?

China mainland, Hong kong and Macau carry out different visa policies, so they are considered as three different regions on this issue. In your case, you need to apply for a single-entry Hong Kong visa and a doule-entry Macau visa if you'll return back to Macau from Hong Kong.
About the Hong Kong tourist visa, photocopy of proof of transportation arrangement, e.g. flight itinerary and photocopy of proof of the proposed leisure visit to Hong Kong, e.g. receipt of joining a package tour to Hong Kong, itinerary, etc are required. I'm not sure if this transportation arrangement means actual air ticket. You may contact the embassy directly for further confirmation: Tel: 84-4-8453736, 903441338; Email: mfa.gov.cn|chinaemb_vn
For macau visa, document of transportation to Macao and accommodation arrangement (e.g. round-trip air ticket and hotel room reservation receipts, etc.) and tour receipt, itinerary, etc are also required. Maybe you can buy the refundable or partially refundable air- ticket.