Ao chegar a casa, lavo a cara com sabonete antes de jantar.

Ao chegar means when arriving, upon arriving, or as soon as I arrive.

In Portuguese, ao + infinitive is a very common way to express time:

• Ao chegar a casa = when I get home
• Ao sair = when leaving
• Ao entrar = upon entering

Grammatically, ao is the contraction of a + o. In this structure, though, it is best learned as a fixed pattern: ao + infinitive = when / upon doing something.

Because Portuguese often leaves out the subject pronoun when it is already clear from the verb ending.

• lavo = I wash
• lavas = you wash
• lava = he/she/you formal washes

So lavo a cara already clearly means I wash my face. Adding eu is possible, but usually unnecessary unless you want emphasis or contrast:

• Eu lavo a cara, mas ele não. = I wash my face, but he doesn’t.

In Portuguese, a casa without an article often means home.

So:

• chegar a casa = to arrive home
• ir a casa = to go home
• voltar a casa = to return home

If you say à casa, it usually means to the house in a more literal or specific sense, and it often needs more context:

• à casa da Maria = to Maria’s house

So in your sentence, chegar a casa is the normal way to say arrive home.

With body parts, Portuguese usually uses the definite article where English uses a possessive.

So:

• lavo a cara = literally I wash the face
• but the real meaning is I wash my face

This is very common:

• Lavo as mãos. = I wash my hands
• Parti o braço. = I broke my arm
• Fecho os olhos. = I close my eyes

Using minha is possible, but it is usually unnecessary unless you want emphasis.

Yes, both cara and rosto can mean face, but they are not used in exactly the same way.

• cara is very common in everyday language
• rosto is a bit more neutral or formal

In daily speech, lavar a cara is a very natural expression for wash one’s face.

So this sentence sounds normal and idiomatic.

Com sabonete means with soap.

In European Portuguese:

• sabonete usually means toilet soap or a bar of soap used on the body
• sabão is a broader word for soap, often associated with cleaning products or laundry soap

So if you are washing your face, com sabonete sounds very natural.

Because antes de + infinitive means before doing something.

Here:

• jantar is the infinitive verb = to have dinner / to eat dinner
• antes de jantar = before having dinner

Compare:

• antes de jantar = before eating dinner
• antes do jantar = before dinner or before the dinner meal/event

Both can be correct, but they are slightly different in structure:

• de + infinitive = before doing something
• de + noun = before something

Because the Portuguese present tense is often used for habitual actions, just like in English.

So:

• Ao chegar a casa, lavo a cara... means something like When I get home, I wash my face...
• It describes a usual action or routine

Portuguese does not need a special tense here. The simple present works perfectly.

Yes. Portuguese allows some flexibility.

For example:

• Ao chegar a casa, lavo a cara com sabonete antes de jantar.
• Lavo a cara com sabonete ao chegar a casa, antes de jantar.

Both are understandable, but the original version is very natural because it starts with the time expression Ao chegar a casa and sets the scene first.

It goes with lavo. It tells you how the face is washed.

So the structure is:

• lavo a cara = I wash my face
• com sabonete = with soap

Together:

• lavo a cara com sabonete = I wash my face with soap

It does not mean that the face itself somehow has soap as a permanent quality; it describes the action.