vudaoece

The best way to learn Spanish, or any foreign language, for that matter, is to totally immerse yourself in the language and culture. Since that may not be an option in Vietnam, the next best thing is to find and befriend some native speakers of Spanish. It appears, based on what you've said, that even this approach to learning would not be an option. Native speakers of Spanish will not always be able to answer questions about grammar, by the way. You would still need to find someone who is able to answer those questions (the forums are a good place for that).

If I were you, my advice would be to find one or more good textbooks, a great teacher, and watch movies or listen to podcasts/radio/songs in Spanish. Try your best to internalize the language and mimic what you're hearing when using aural media.