En el porche dejamos las botas mojadas para no ensuciar la entrada.

It can mean either one.

For -ar verbs, the nosotros form of the present and the preterite is often identical:

• dejamos = we leave
• dejamos = we left

So this sentence by itself is ambiguous. Only the context tells you which meaning is intended.

Examples:

• Cada día, en el porche dejamos las botas mojadas... = Every day, we leave the wet boots on the porch...
• Ayer, en el porche dejamos las botas mojadas... = Yesterday, we left the wet boots on the porch...

This is very normal in Spanish.

Spanish often drops subject pronouns because the verb ending already shows who the subject is.

• dejamos already tells you the subject is we
• So nosotros dejamos is possible, but usually unnecessary

You would add nosotros only for emphasis, contrast, or clarity:

• Nosotros dejamos las botas, no ellos = We left the boots, not them

In a neutral sentence, leaving the pronoun out sounds more natural.

Because en tells you the location where the boots were left.

• en el porche = on/in the porch area, on the porch
• al porche would suggest movement to the porch

Compare:

• Dejamos las botas en el porche = We left the boots on the porch
• Fuimos al porche = We went to the porch

Here the important idea is the place where the boots ended up, so en is the natural choice.

Yes, porche is masculine, so it takes el:

• el porche

This is just something you learn with the noun. The ending -e does not automatically tell you whether a noun is masculine or feminine, so the article matters.

Other examples with -e:

• el coche
• la calle
• el puente

So the gender has to be learned word by word.

In Spanish, adjectives usually come after the noun.

• las botas mojadas = the wet boots

Also, the adjective must agree with the noun:

• botas is plural
• botas is feminine
• so the adjective becomes mojadas

Agreement pattern:

• bota mojada
• botas mojadas
• zapato mojado
• zapatos mojados

Putting the adjective before the noun is sometimes possible in Spanish, but it usually changes the tone or sounds literary/emphatic. In this sentence, the normal order is las botas mojadas.

Spanish often uses the definite article instead of a possessive when ownership is obvious from the context.

So:

• dejamos las botas mojadas naturally means we left our/the wet boots

Because the subject is we, it is easy to understand whose boots they are.

This is very common in Spanish:

• Me lavé las manos = I washed my hands
• Se puso el abrigo = He/She put on his/her coat

Using nuestras botas is possible, but it sounds more explicit and is not necessary unless you want to stress ownership.

Para + infinitive is the normal way to express purpose when the subject is the same or when the subject is general.

• para no ensuciar la entrada = so as not to dirty the entrance

The structure is:

• para = in order to / so as to
• no ensuciar = not to dirty

It works very much like English to or in order to.

Examples:

• Salí temprano para llegar a tiempo = I left early to arrive on time
• Guardamos silencio para no despertar al bebé = We kept quiet so as not to wake the baby

If Spanish needs to introduce a different subject, it often uses para que + subjunctive instead:

• Te lo digo para que lo sepas = I’m telling you so that you know it

But here para no ensuciar is the natural structure.

Ensuciar means to make dirty, to dirty, or to soil.

In this sentence:

• para no ensuciar la entrada = so as not to dirty the entrance

It focuses on causing something to become dirty.

A useful comparison:

• estar sucio = to be dirty
• ensuciar = to make something dirty

Examples:

• Los niños ensuciaron la pared = The children dirtied the wall
• No ensucies el suelo = Don’t dirty the floor

So the idea is that the wet boots might make the entrance dirty.

Here la entrada means the entrance area of the house, not the physical door itself.

Depending on context, la entrada can be:

• the entrance
• the entryway
• the hall
• the area just inside the door

It usually does not mean the door. That would be:

• la puerta

So:

• ensuciar la entrada = to dirty the entrance/entryway
• ensuciar la puerta = to dirty the door

In this sentence, the idea is that the boots are left on the porch so mud or water does not get into the entrance area.

Because no negates the infinitive:

• para ensuciar = to dirty
• para no ensuciar = not to dirty / so as not to dirty

This is exactly how Spanish normally negates an infinitive:

• Intento no llegar tarde = I try not to arrive late
• Salió sin no? No. After sin, you use just the infinitive: Salió sin decir nada = He/She left without saying anything
• Es importante no olvidar eso = It’s important not to forget that

So here no simply means the purpose is to avoid making the entrance dirty.

Yes. Spanish en is broader than English in.

With places, en can often correspond to:

• in
• on
• at

So:

• en el porche is naturally translated as on the porch

This is normal and not a word-for-word problem. Translation depends on what sounds natural in English, not just on the single preposition.

Examples:

• en la playa = at the beach
• en la mesa = on the table
• en casa = at home / home

So en el porche → on the porch is exactly what you would expect in natural English.