If you mean to say "What should we say when we begin speaking with a tourist?" then I would suggest "Hi, my name is ____ where are you from?" "Is there anything I can help you find?" "What brings you to Viet Nam?"

As a tourist in an English speaking country, you want to learn basics such as: Excuse me, please, thank you, hello, good bye Other situations you need to prepare for are language for asking and giving directions and for buying things (at store, market, restaurant) or for renting (cars or hotel rooms). Your best option for practice would be to find someone who wants to learn Vietnamese and exchange 50/50 sessions with him/her on Skype. See here: https://www.facebook.com/pages/English-for-Vietnamese/112224838805157