La guillotina corta el cartón gris.

Because la guillotina means the guillotine or the cutter, not a guillotine.

In Spanish:

• la = the (feminine singular)
• una = a / an (feminine singular)

So:

• La guillotina = the guillotine
• Una guillotina = a guillotine

Spanish often uses the definite article very naturally when talking about a specific thing already understood from the context.

Yes. Guillotina is a feminine noun, so it takes the feminine article la.

You can usually tell from the article:

• el cartón
• la guillotina

A lot of nouns ending in -a are feminine, and guillotina follows that common pattern.

Because cartón is a masculine singular noun.

So the correct definite article is:

• el for masculine singular
• la for feminine singular

That gives:

• el cartón = the cardboard

Lo is not used as a normal article before nouns. It has other uses in Spanish, but not here.

Corta is the third-person singular present tense of cortar.

The infinitive is:

• cortar = to cut

Present tense:

• yo corto
• tú cortas
• él / ella / usted corta
• nosotros / nosotras cortamos
• vosotros / vosotras cortáis
• ellos / ellas / ustedes cortan

In this sentence, the subject is la guillotina, which is singular, so the verb must be corta.

Because here corta is a verb, not an adjective.

Spanish corta can be:

• a form of the verb cortar = cuts
• a feminine form of the adjective corto = short

In this sentence:

• La guillotina corta el cartón gris the word corta comes between the subject and the object, so it is understood as the verb: cuts.

If it were an adjective, the structure would be different, for example:

• La falda corta = the short skirt

In Spanish, adjectives usually come after the noun.

So:

• cartón gris = grey cardboard

This is the most normal position for a descriptive adjective in Spanish. English usually puts adjectives before the noun, but Spanish often places them after it.

Because gris is one of the adjectives that often has the same form in masculine and feminine singular.

So you can have:

• el cartón gris
• la caja gris

The plural does change:

• los cartones grises
• las cajas grises

So gris does show number, but in the singular it stays the same for masculine and feminine.

It describes cartón.

In:

• La guillotina corta el cartón gris the phrase el cartón gris is a noun phrase meaning the grey cardboard.

So:

• el cartón = the cardboard
• gris = grey

It does not mean that the guillotine is grey.

The accent mark shows which syllable is stressed: car-TÓN.

Without the accent, Spanish stress rules would make you pronounce it differently. The written accent tells you clearly that the stress falls on the last syllable.

So:

• cartón → stress on -tón

This is important both for pronunciation and spelling.

A careful Spain Spanish pronunciation would be roughly:

la gee-yo-TEE-na KOR-ta el kar-TON grees

A bit more precisely:

• La = la
• guillotina = gi-yo-ti-na
  In Spain, ll is commonly pronounced like an English y sound.
• corta = KOR-ta
• el = el
• cartón = kar-TON
• gris = grees

A natural rhythm would stress:

• gui-llo-TI-na
• COR-ta
• car-TÓN
• gris

Sometimes yes, but in everyday modern Spanish it can also refer to a paper cutter or cutting machine, depending on context.

So in a sentence with cartón (cardboard), many learners would naturally understand guillotina as a cutting device used for paper or cardboard, not necessarily the historical execution device.

Context matters a lot.

Yes, Spanish word order is flexible, but the neutral, most standard order here is:

• La guillotina corta el cartón gris.

That is:

• subject + verb + object

You could sometimes change the order for emphasis, but that would sound less neutral. For a learner, the original order is the best one to use.

Yes, Spanish often omits the subject when it is clear from context.

So:

• Corta el cartón gris
  can mean It cuts the grey cardboard or he/she cuts the grey cardboard, depending on context.

Spanish is a pro-drop language, which means subject pronouns and even full subjects are often left out when the verb already gives enough information.

But in your sentence, La guillotina is included to make the subject explicit.

Because Spanish does not need an extra helper verb here.

English often uses does in questions or emphasis:

• The guillotine does cut the grey cardboard

But in a normal statement, English simply says:

• The guillotine cuts the grey cardboard

Spanish works similarly here:

• La guillotina corta el cartón gris

And there is no is because this sentence is an action sentence, not a description like The cardboard is grey.

If everything became plural, it would be:

• Las guillotinas cortan los cartones grises.

Changes:

• la → las
• guillotina → guillotinas
• corta → cortan
• el → los
• cartón → cartones
• gris → grises

This shows agreement in articles, nouns, verbs, and adjectives.