Mi hermano estadounidense alquila una bicicleta.

Mi means my. In Spanish, possessive words like mi, tu, su, nuestro are used before the noun, just like in English.

So:

• mi hermano = my brother
• el hermano = the brother
• un hermano = a brother

Here, mi shows who the brother belongs to or is related to.

Because before a noun, Spanish uses the short possessive form:

• mi hermano = my brother

The longer form mío is usually used after a noun or by itself:

• Este hermano es mío = This brother is mine

So directly before a noun, you say mi, not mío.

Estadounidense means from the United States or American in the sense of U.S. American.

Many Spanish speakers use estadounidense because it is more specific than americano, since América can refer to the whole continent or the Americas in Spanish.

So:

• mi hermano estadounidense = my American brother / my brother from the United States

In Spanish, adjectives often come after the noun.

So:

• hermano estadounidense = American brother
• literally: brother American

This is the normal placement for nationality adjectives in Spanish:

• una actriz mexicana
• un profesor chileno
• mi amigo colombiano

Some Spanish adjectives change form for masculine and feminine, but estadounidense is an adjective with the same form for both genders.

So you get:

• mi hermano estadounidense
• mi hermana estadounidense

Compare that with an adjective that does change:

• mi hermano mexicano
• mi hermana mexicana

So estadounidense already agrees correctly even though it does not visibly change.

Because bicicleta is a feminine singular noun, so it takes the feminine singular indefinite article una.

• una bicicleta = a bicycle

Spanish articles must agree with the noun in gender and number:

• un libro
• una casa
• unos libros
• unas casas

Since bicicleta is feminine, una is the correct article.

Usually, nouns ending in -a are feminine, and bicicleta follows that common pattern.

So:

• la bicicleta
• una bicicleta

Like many Spanish nouns, grammatical gender is something you learn together with the word. A good habit is to memorize nouns with their article:

• la bicicleta, not just bicicleta

Alquila is the third-person singular present tense form of the verb alquilar.

Conjugation:

• yo alquilo
• tú alquilas
• él/ella/usted alquila
• nosotros/nosotras alquilamos
• ellos/ellas/ustedes alquilan

Since the subject is mi hermano, which is third-person singular, the correct form is alquila.

It can mean to rent in the sense of to hire or to rent something for your own use. In many contexts, alquilar una bicicleta means to rent a bicycle.

Depending on context, alquilar can also mean to rent out something, but here the meaning is clearly that the brother is the person obtaining the bicycle for temporary use.

So in this sentence:

• alquila una bicicleta = rents a bicycle

Spanish often omits subject pronouns because the verb ending already tells you the person and number.

So instead of saying:

• Él alquila una bicicleta

Spanish can simply say:

• Alquila una bicicleta

In this sentence, the subject is already stated as Mi hermano estadounidense, so adding él would be unnecessary unless you wanted emphasis or contrast.

That would sound unnatural in normal Spanish.

The natural order is:

• Mi hermano estadounidense

In Spanish, most descriptive adjectives, especially nationality adjectives, come after the noun. Putting estadounidense before hermano would sound very unusual and not like standard everyday Spanish.

In Spanish, adjectives of nationality are not capitalized.

So Spanish writes:

• estadounidense
• mexicano
• argentino

This is different from English, where nationality words are capitalized:

• American
• Mexican
• Argentine / Argentinian

A simple approximation is:

• ahl-KEE-lah

More closely:

• a as in father
• qui sounds like kee
• la sounds like lah

The stress is on the second syllable: qui.

So: al-QUI-la

In most of Latin America, ll is pronounced like y in English yes.

So alquila sounds roughly like:

• al-kee-la, with the ll sounding like y

In some regions, the sound can vary a little, but for most learners, thinking of ll = y is a very good starting point.

Yes, but it changes the meaning.

• una bicicleta = a bicycle (any bicycle, not specific)
• la bicicleta = the bicycle (a specific bicycle already known in context)

So:

• Mi hermano estadounidense alquila una bicicleta = he rents a bicycle
• Mi hermano estadounidense alquila la bicicleta = he rents the bicycle

The original sentence uses una because it introduces a non-specific bicycle.

It is one person.

The subject is the noun phrase:

• mi hermano estadounidense

That whole phrase means my American brother.

The structure is:

• mi = my
• hermano = brother
• estadounidense = American / from the U.S.

So all three parts refer to the same person.

Yes, in some contexts hermano can be used figuratively, like brother in religion, friendship, or solidarity. But in a basic sentence like this, learners should normally understand it as the literal family meaning: brother.

So here, the most natural reading is simply:

• my American brother rents a bicycle