hello, your question is quite generic, may you specify the route you are going to take? in general, it is easy to book an internal air ticket. just visit Vietnam airline website or Guidevietnam.com for e-ticket booking.
Answers: How to book a flight between Vietnam?
I wud like to book a ticket from Ho Chi Mien to Hanoi (return ticket) for April 14 and return on April 16, 2011. And pls inform me about the air tax. Thank you