Antes de imprimir, usé el subrayador para marcar el encabezado y la primera página del informe.

In Spanish, antes is followed by de when the next verb is in the infinitive:

• antes de imprimir
• antes de salir
• antes de comer

So antes de + infinitive means before doing something.

If the clause has a different subject, Spanish often uses antes de que + subjunctive instead:

• Antes de que imprimieras el informe, yo lo revisé.

Here, antes de imprimir works because it means before printing in a general way, with no separate subject stated.

Usé is the 1st person singular preterite of usar: I used.

The preterite is used here because the sentence refers to a completed action in the past:

• usé = I used
• a specific action, finished before the next stage

So the sentence presents a sequence:

1. I used the highlighter/tool
2. then printing happened later

If it said usaba, that would sound more like a repeated or ongoing past action:

• Antes de imprimir, usaba el subrayador...
  = Before printing, I used to use the highlighter... / I was using...

That does not fit as well here.

The accent mark distinguishes usé from use.

• usé = I used (preterite, yo)
• use = form of usar in the present subjunctive or formal command contexts

So the accent helps show both pronunciation and grammar.

A few similar examples:

• hablé = I spoke
• compré = I bought
• terminé = I finished

This is a very common pattern for regular -ar verbs in the yo preterite.

Subrayador comes from subrayar, meaning to underline or sometimes more broadly to highlight/mark depending on context.

It can refer to:

• a highlighter pen
• an underlining tool in a digital document
• something used to mark text

A learner may also see other words depending on region and context, such as:

• resaltador
• marcador fluorescente

In Spain, the most natural choice can vary by context, but subrayador is understandable as something used to mark text.

Para + infinitive expresses purpose: in order to / to.

So:

• usé el subrayador para marcar...
• I used the highlighter/tool to mark...

It answers the question what for?

Other examples:

• Abrí el archivo para revisarlo.
• Llamé para confirmar la cita.

So para marcar explains the purpose of using the subrayador.

Good question. Both can make sense, but they are slightly different.

• subrayar = to underline
• marcar = to mark

Marcar is more general. It can mean highlighting, marking, indicating, or making something stand out.

So the sentence may be using subrayador as the tool and marcar as the broader action. That leaves open exactly how the text was marked.

If the speaker wanted to be more specific, they could say:

• usé el subrayador para subrayar el encabezado...

But marcar is not wrong; it is just more general.

Encabezado is a masculine noun, so it takes el:

• el encabezado

It means heading or header, depending on context.

Some related words:

• el título = the title
• el encabezado = the heading/header
• la cabecera = header/top section, also used in some contexts

A learner may notice that English sometimes prefers title where Spanish uses encabezado, depending on the document.

Because página is feminine:

• la primera página

The shortened form primer is used only before masculine singular nouns:

• el primer día
• el primer capítulo

But with feminine nouns, you keep the full form:

• la primera página
• la primera vez

So primer página would be incorrect here.

Because in Spanish, de + el contracts to del.

So:

• de + el informe → del informe

This is a standard contraction.

The two main mandatory contractions are:

• a + el = al
• de + el = del

But note that this does not happen with la:

• de la página
• a la oficina

Grammatically, del informe most directly attaches to the nearest noun phrase, so it most naturally sounds like:

• the first page of the report

In other words:

• el encabezado
• y la primera página del informe

However, in real context, a reader might understand that both the heading and the first page belong to the report.

If you wanted to make it completely clear that both belong to the report, you could rephrase:

• ...para marcar el encabezado del informe y la primera página.
• ...para marcar el encabezado y la primera página del informe
  (current version, a bit more naturally tied to the second noun)

So the original is fine, but the attachment is slightly clearer for the second item.

Spanish often avoids repetition when the meaning is clear.

So instead of saying:

• el encabezado del informe y la primera página del informe

it is more natural to say:

• el encabezado y la primera página del informe

This is normal and common. Spanish, like English, often lets one final phrase cover part of a coordinated expression if the context is clear enough.

The comma separates the introductory phrase from the main clause:

• Antes de imprimir,
• usé el subrayador...

This is similar to English punctuation with an opening time phrase:

• Before printing, I used...

In Spanish, this comma is very natural and helps readability, especially when the introductory phrase comes first.