Mi tía usa pintalabios rojo cuando sale a cenar.

In modern standard Spanish, you normally use the short possessive directly before the noun:

• mi tía = my aunt
• tu casa = your house
• su coche = his/her/their car

Using la mi tía is not standard in normal modern Spanish. You may occasionally see longer possessive forms such as la mía, but those are used differently, usually after a noun or on their own:

• Esta tía es mía = This aunt is mine
• Mi tía = My aunt

So here, mi tía is exactly what you would expect.

The accent in tía shows that the i and a are pronounced in two separate syllables:

• tí-a

Without the accent, tia would suggest a different pronunciation pattern. The written accent tells you that the í is stressed and forms a hiatus rather than blending into one syllable.

This is very common in words like:

• día
• frío
• país
• tía

So the accent is there to guide pronunciation and stress.

Usa is the third-person singular present tense of usar (to use / to wear in some contexts).

Here it refers to mi tía, which is she, so:

• yo uso = I use
• tú usas = you use
• él/ella usa = he/she uses

In this sentence, the present tense is being used for a habitual action:

• Mi tía usa pintalabios rojo cuando sale a cenar.
• My aunt wears red lipstick when she goes out for dinner.

It does not necessarily mean she is doing it right now; it can describe what she generally does.

Spanish often omits subject pronouns because the verb ending already tells you who the subject is.

Here, usa already shows he/she/it uses, so ella is not necessary:

• Mi tía usa... = My aunt uses/wears...
• Ella usa... would also be possible, but it is usually unnecessary unless you want emphasis or contrast.

Spanish does this much more than English. In English, you usually need she; in Spanish, you often do not.

Pintalabios means lipstick.

In Spain, pintalabios is a very common word. You may also hear:

• barra de labios
• lápiz labial (more common in some other Spanish-speaking regions)

So for Spain Spanish, pintalabios sounds very natural.

This is a very common question. Even though pintalabios ends in -s, it is often a singular noun.

So:

• un pintalabios = a lipstick
• dos pintalabios = two lipsticks

The form often stays the same in singular and plural, and the article or context tells you whether it is singular or plural.

In this sentence, pintalabios is singular because it refers to the product in a general sense: red lipstick.

Because rojo agrees with pintalabios, and pintalabios is treated as a masculine noun.

So:

• pintalabios rojo = red lipstick
• vestido rojo = red dress
• casa roja = red house

Even though lipstick may seem like an object you might expect to be feminine, grammatical gender in Spanish depends on the noun, not on the thing itself. Since pintalabios is masculine, the adjective is rojo.

Both are possible, but they feel slightly different.

• usa pintalabios rojo = she wears/uses red lipstick, speaking more generally
• usa un pintalabios rojo = she wears a red lipstick / a red lipstick, which sounds a bit more like one specific item or one instance

When talking about cosmetics, clothing, or things someone typically wears, Spanish often leaves out the article in a fairly general statement.

So this sentence is natural if the idea is simply:

• She wears red lipstick when she goes out to dinner.

If you wanted to focus on one particular lipstick, un pintalabios rojo would also work.

Yes. Usar is perfectly possible here and means to use or, in context, to wear.

With clothes, accessories, and cosmetics, Spanish can use several verbs depending on nuance:

• usar = to use / wear
• llevar = to wear
• ponerse = to put on

So these are all possible in different contexts:

• Mi tía usa pintalabios rojo = My aunt wears/uses red lipstick
• Mi tía lleva pintalabios rojo = My aunt is wearing red lipstick
• Mi tía se pone pintalabios rojo = My aunt puts on red lipstick

Here, usa sounds like a general habit.

It means when she goes out to dinner.

Breakdown:

• cuando = when
• sale = she goes out / leaves
• a cenar = to have dinner / to eat dinner

Together, salir a cenar is a very common expression meaning:

• to go out for dinner
• to go out to eat dinner

So this is not just leave and then eat in a literal word-by-word sense; it is an idiomatic expression.

Because salir a cenar specifically suggests going out for dinner.

Compare:

• ir a cenar = to go to have dinner
• salir a cenar = to go out to dinner

Salir adds the idea of going out, often socially or to a restaurant. That fits the context very well here.

So:

• cuando sale a cenar = when she goes out for dinner
• cuando va a cenar could sound less specific and less idiomatic in this context

Because this sentence is describing a real, habitual action, not something hypothetical, desired, or uncertain.

• cuando sale a cenar = when she goes out to dinner

Spanish often uses the indicative after cuando when talking about something habitual or repeated.

You would use the subjunctive more often if the action is in the future or not yet realized:

• Cuando salga a cenar, usará pintalabios rojo.
• When she goes out to dinner, she will wear red lipstick.

But in your sentence, the idea is general and habitual, so sale is correct.

We understand that mi tía is also the subject of sale.

In Spanish, when there is no new subject introduced, the subject usually stays the same:

• Mi tía usa pintalabios rojo cuando sale a cenar.

The natural reading is:

• My aunt wears red lipstick when she goes out to dinner.

If the subject changed, Spanish would usually make that clear:

• Mi tía usa pintalabios rojo cuando mi madre sale a cenar.
• My aunt wears red lipstick when my mother goes out to dinner.

So in your sentence, sale clearly refers back to mi tía.

Normally, no. In this case, the natural order is:

• pintalabios rojo

Color adjectives usually come after the noun in Spanish:

• coche rojo = red car
• camisa blanca = white shirt
• pintalabios rojo = red lipstick

Putting rojo before the noun would sound unusual or poetic, and with this noun it would not be the normal choice at all.

Yes, especially because of pintalabios, which is very common in Spain.

A learner might also hear other regional equivalents in the Spanish-speaking world, such as:

• labial
• lápiz labial
• barra de labios

But if your focus is Spanish from Spain, pintalabios is a very natural word to know.