Note that prepostion + article are used as well to mark the indirect object, a, or the genitive, de.
Furthermore it is useful to see, in order to avoid confusions, that the article and the personal pronouns as a direct object have the same form.
I see her.
The first a, in yellow, is an article feminine singular. The second a, in orange, is a pronun, direct object feminine singular. We don't care right now that a personal pronoun, in opposite to any other roman language, stand after the verb, we will discuss this issue later.
article singular masculine + pronoun third person singular masculine direct object
article singular feminine + pronoun third person singular feminine direct object
article Plural masculine + pronoun third person plural masculine direct object
article Plural feminine + pronoun third person plural feminine direct object
Furthermore one should see that a / as (preposition) + a article / pronoun fuse to à, às. This accent is not a diacritical sign, has nothing to do with the pronunciation. It has a purely grammatical function.
In the example we provide the gender, although it is not necessary in most cases, because words ending in a are feminine in general, words ending in o are masculine.