In Spanish, adjectives usually go after the noun, but they can go before it. For example, you can say 'mi viejo amigo' or 'mi amigo viejo'.
In English, adjectives go BEFORE the noun. You have to say 'an interesting country'. You can't put 'interesting' after 'country'.
And if the word after 'a' begins with vowel sound, we say 'an', not 'a'.