Ivan makes a good point when he says that "our" can be sometimes be distinguished by its sound. In most dialects of American English, it sounds like "are" and rhymes with car, bar, star, etc. But even without a different sound, it's not very hard to distinguish between either of those pairs of words from the context. "Our" is a possessive adjective (como "nuestro") and "hour" is a countable noun. "Our" is always followed by a noun, and "hour" never is. "Flour" is always an uncountable noun, so it is never proceeded by "a" or "an" and it is never plural. "Flower" is a countable noun, so it will usually either be preceded by "a" or "an" (or sometimes by another type of determiner) or be in its plural form.

You usually only know from context. In English, even native speakers get words confused if they don’t hear the full context. For these words specifically though, you only see “our” used alone, but “hour” is used with an article like “an hour” or “the hour.” The word “flour” is special because the plural is also “flour.” If you hear the word with an “s” at the end, it can only be “flowers” because “flours” is not a word. Examples: This is our house I’ll see you in an hour She made a cake and had flour in her hair She looked pretty with flowers in her hair

Dependa on the context