Antes do jantar, passo a escova pelo cabelo e lavo as mãos.

Literally, passo a escova pelo cabelo means “I pass the brush through my hair.”

• passo = “I pass”
• a escova = “the brush”
• pelo cabelo = “through the hair” (see next question for pelo)

By contrast, escovo o cabelo uses the verb escovar (“to brush”), so it means “I brush my hair.”

• passar a escova pelo cabelo focuses on the action of moving the brush through the hair, often emphasizing the instrument.
• escovar o cabelo is more direct, treating brushing as a single action. Both are correct and commonly heard in Portugal.

• antes do jantar = “before dinner,” where do is the contraction of de + o (the definite article).
• Using antes de jantar (“before having dinner”) is also acceptable and very common, especially in spoken Portuguese.

Nuance:
• antes do jantar often refers to a specific meal (e.g., “the dinner we always have at 8 pm”).
• antes de jantar is more general and slightly more abstract (“before eating dinner”).

pelo is a contraction of por + o.

• por here means “through” or “over.”
• o cabelo = “the hair.”

So pelo cabelo = “through the hair” or “over the hair,” depending on context.

Portuguese normally uses the definite article with body parts:

• lavo as mãos = “I wash (the) hands” = “I wash my hands.”

Omitting the article (saying lavo mãos) sounds very unnatural. You could use a possessive instead: lavo as minhas mãos, but it’s redundant unless you’re contrasting (e.g., “I wash my hands, not yours”).

Absolutely. Both orders work:
• Antes do jantar, passo a escova pelo cabelo e lavo as mãos.
• Passo a escova pelo cabelo e lavo as mãos antes do jantar.

Putting antes do jantar at the beginning emphasizes the time frame; at the end, it sounds more neutral or conversational.

The simple present (passo, lavo) describes habitual or routine actions, which fits well if you do this every evening.
Alternatives:

• Present continuous (European Portuguese less often uses it): estou a passar a escova… e a lavar as mãos (more formal or highlighting the action in progress).
• Near future: vou passar a escova… e vou lavar as mãos (if you mean “I’m going to brush…” immediately).

But for routines, the simple present is both correct and most natural.