Usamos la plegadera para prensar la guarda.

Spanish often leaves out the subject pronoun when the verb ending already makes the subject clear.

• usamos = we use
• The ending -amos tells you it is we.

So Usamos la plegadera... is completely natural. You could say Nosotros usamos la plegadera..., but that usually adds emphasis or contrast, for example:

• Nosotros usamos la plegadera, no la espátula.
  = We use the bone folder, not the spatula/tool.

Usamos is the present indicative, first person plural, from usar.

• yo uso = I use
• tú usas = you use
• él/ella usa = he/she uses
• nosotros/nosotras usamos = we use
• vosotros/vosotras usáis = you all use
• ellos/ellas usan = they use

In a sentence like this, the present can sound like:

• a general statement: We use...
• a step in a process/instructions: We use...

That instructional use is very common in Spanish.

La plegadera is a specific tool, especially in bookbinding and paper work. In English, it is often called a bone folder.

It is feminine because the noun is feminine:

• la plegadera

This does not mean it is feminine in any real-world sense; it is just grammatical gender.

The word comes from the idea of folding or creasing paper or material. In this context, it refers to the tool used to smooth, fold, or press.

Spanish uses the definite article much more often than English.

So where English might say:

• We use a bone folder
• or We use the bone folder

Spanish often says:

• Usamos la plegadera

Here, la can sound natural even if English might prefer a in a general description. In technical instructions, Spanish often treats the tool as the expected or standard one for the task.

Para expresses purpose: in order to, to, for the purpose of.

After para, Spanish uses the infinitive when the subject does not need to change.

So:

• para prensar = to press
• literally: in order to press

This structure is very common:

• Usamos X para cortar. = We use X to cut.
• Usamos X para doblar. = We use X to fold.

Both relate to pressing, but prensar is more specific and often more technical.

• prensar = to press, compress, clamp, press together
• presionar = to apply pressure, press on, put pressure on

In bookbinding or craft contexts, prensar often sounds more appropriate because it suggests firm pressing/compression as part of the process.

So in this sentence, prensar is likely the more idiomatic technical verb.

In everyday Spanish, guarda can have several meanings in different contexts, but here it is a bookbinding term.

In this context, la guarda refers to the endpaper or a related inner paper part of a book structure.

So this is specialized vocabulary. A learner might recognize guardar or guardia and think of keeping or guarding, but that is not the meaning here. This is one of those cases where a word has a technical meaning in a craft.

Again, Spanish uses articles very naturally with concrete nouns, especially when talking about a specific part being worked on.

• la guarda = the endpaper / the guard

In workshop or instructional language, this usually means the specific piece you are working with at that moment, not just the concept in general.

The given word order is very natural:

• Usamos la plegadera para prensar la guarda.

But Spanish word order is flexible, especially for emphasis. For example:

• Para prensar la guarda, usamos la plegadera.
• La plegadera la usamos para prensar la guarda.

These alternatives are possible, but the original version is the most neutral and straightforward.

Yes. In Spanish, especially in explanations, demonstrations, and manuals, it is common to use first person plural:

• Usamos...
• Colocamos...
• Pegamos...

This has an inclusive feel, like we now do this step. English instructions often prefer the imperative or a more impersonal style, but Spanish commonly uses this instructional we.

If you wanted to turn it into a direct instruction, you could say:

• Usa la plegadera para prensar la guarda. = Use the bone folder to press the endpaper.
• Usad la plegadera para prensar la guarda. = Use the bone folder... (plural vosotros, common in Spain)
• Use la plegadera para prensar la guarda. = formal singular
• Usen la plegadera para prensar la guarda. = formal plural / Latin American plural

The original Usamos... is less like a direct order and more like guided instruction or explanation.