Sello la caja con cinta.

Yes. Sello can be:

• a noun: stamp, seal
• a verb form from sellar: I seal

In Sello la caja con cinta, sello is the first-person singular present form of sellar, so it means I seal or I am sealing depending on context.

Spanish often has forms that look identical as nouns and verbs, so the rest of the sentence tells you which one it is.

Spanish often omits subject pronouns because the verb ending already shows who is doing the action.

• sello = I seal
• so yo is not necessary

You could say Yo sello la caja con cinta, but it usually sounds more natural to leave yo out unless you want to add emphasis, contrast, or clarity.

For example:

• Yo sello la caja, y tú etiquetas los paquetes.
  = I seal the box, and you label the packages.

La caja is the direct object. It is the thing receiving the action of the verb.

• sellar = to seal
• la caja = the box

So the action is being done to the box.

Also, la is the feminine singular definite article because caja is a feminine noun:

• el libro
• la caja

In Spanish, articles like el, la, un, and una are used more often than in English. So where English might sometimes say I seal boxes or I seal the box, Spanish often prefers an article.

Here, la caja means the box. It sounds complete and natural.

If you said just Sello caja, it would sound incomplete or unnatural in standard Spanish.

Con means with, and cinta here means tape.

So con cinta tells you the means or material used to seal the box:

• Sello la caja con cinta. = I seal the box with tape.

This is very common in Spanish:

• Corto el pan con un cuchillo. = I cut the bread with a knife.
• Escribo con lápiz. = I write with a pencil.

Because in this sentence cinta is being used in a general/material sense, similar to saying:

• with tape
• with glue
• with string

Spanish often leaves out the indefinite article when talking about a material or tool in a general way.

So:

• con cinta = with tape
• con una cinta would sound more like with a ribbon / with one strip of tape / with a specific tape, depending on context

In Latin American Spanish, cinta can mean tape, and in packaging contexts that is very natural.

Yes. Cinta can have several meanings depending on context, such as:

• tape
• ribbon
• band
• sometimes part of set expressions

But in Sello la caja con cinta, the context strongly points to tape, especially packing tape or sealing tape.

If the speaker wanted to be extra specific, they might say:

• cinta adhesiva = adhesive tape
• cinta de embalaje = packing tape

Yes, the normal, neutral order is:

• verb + object + phrase
• Sello la caja con cinta

This is the most natural way to say it.

You can change the order for emphasis, but it may sound marked:

• Con cinta sello la caja.
  = With tape, I seal the box.

That version emphasizes con cinta.

Spanish word order is flexible, but the standard order here is the clearest and most common.

Yes. Sello is the present indicative of sellar.

In Spanish, the simple present can translate into English in more than one way depending on context:

• I seal the box with tape
• I am sealing the box with tape

If you want to clearly stress the ongoing action, Spanish can also use the progressive:

• Estoy sellando la caja con cinta.

But the simple present is extremely common and natural.

The structure tells you.

In the sentence:

• Sello = conjugated verb
• la caja = object
• con cinta = prepositional phrase

That is a normal verb sentence pattern. If sello were a noun, the sentence would need a different structure.

For example:

• El sello está sobre la mesa. = The stamp/seal is on the table.

So grammar helps you tell whether sello is a noun or a verb.

Yes, a Latin American speaker could absolutely say Sello la caja con cinta. It is grammatical and natural.

Depending on the exact situation, people might also say:

• Cierro la caja con cinta. = I close the box with tape.
• Pego la caja con cinta. = I tape the box / I stick it with tape.
• La sello con cinta. = I seal it with tape.

The best verb depends on whether you want to stress:

• sealing it shut
• closing it
• putting tape on it

But sellar works very well for the idea of sealing a box.

In Latin American Spanish, sello is pronounced approximately like:

• SEH-yo

Details:

• se sounds like seh
• ll in most of Latin America sounds like y in yes
• the stress is on the first syllable: SE-llo

So:

• sello → SEH-yo
• caja → roughly KA-ha in most Latin American accents
• cinta → SEEN-ta

A rough full pronunciation would be:

• SEH-yo la KA-ha kon SEEN-ta

Yes. Since la caja is a feminine singular direct object, you can replace it with la:

• La sello con cinta. = I seal it with tape.

That is very natural if the box has already been mentioned.

This is a useful pattern:

• Compro la mesa → La compro
• Cierro la puerta → La cierro
• Sello la caja → La sello