Dejé el taburete junto al balcón para poner el cactus sobre el alféizar.

Dejé is the preterite form of dejar, used for a completed action in the past: I left / I placed.

In this sentence, the speaker is describing one finished action:

• Dejé el taburete... = I left/put the stool...

Why not the others?

• dejaba = imperfect, often used for repeated actions, background description, or something ongoing in the past
  
  • Dejaba el taburete junto al balcón cada mañana = I used to leave the stool next to the balcony every morning
• he dejado = present perfect, common in Spain for a recent past action connected to the present
  
  • He dejado el taburete junto al balcón = I’ve left the stool next to the balcony

So dejé simply tells you the action happened and is complete.

Here dejar means something like to leave, to put, or to place and leave somewhere.

So:

• Dejé el taburete junto al balcón = I left / put the stool next to the balcony

It is not necessarily the same as just put in English. Dejar often suggests that you place something somewhere and it stays there.

Compare:

• Puse el taburete junto al balcón = I put the stool next to the balcony
• Dejé el taburete junto al balcón = I left the stool next to the balcony

Both can work, but dejar emphasizes the resulting position a bit more.

Because junto a is the fixed expression.

• junto a = next to / beside
• a + el = al

So:

• junto a el balcón becomes junto al balcón

You do not say junto del balcón here, because the preposition required is a, not de.

Examples:

• junto a la puerta = next to the door
• junto al sofá = next to the sofa

These are all location expressions, but they are not exactly the same.

• junto a = right next to / beside
• al lado de = next to / at the side of
• cerca de = near, but not necessarily immediately next to

So in this sentence:

• junto al balcón suggests the stool is right by the balcony
• al lado del balcón would be very similar
• cerca del balcón would mean only near the balcony, possibly with some distance

For this sentence, junto al balcón is more precise than cerca del balcón.

Spanish often uses the definite article more broadly than English does.

Here, el appears because the speaker is referring to specific, identifiable things in the situation:

• el taburete = the stool
• el cactus = the cactus
• el alféizar = the windowsill

Even if English might sometimes say a stool or omit an article in a different context, Spanish often prefers the article when the object is known or understood.

Also, in this sentence the objects sound specific:

• the stool the speaker used
• the cactus being moved
• the windowsill in question

Para + infinitive expresses purpose: in order to, so as to.

So:

• para poner el cactus sobre el alféizar = to put the cactus on the windowsill / in order to put the cactus on the windowsill

This tells us why the speaker left the stool next to the balcony.

Without para, the relation would be unclear or ungrammatical in this structure. Spanish normally needs para to express this kind of purpose when the subject is the same:

• Fui a la cocina para beber agua
• Moví la silla para abrir la ventana

Because the sentence names the object directly: el cactus.

• poner el cactus = to put the cactus

You could use a pronoun if the context already made it clear:

• ...para ponerlo sobre el alféizar = ...to put it on the windowsill

But Spanish often keeps the noun instead of replacing it with a pronoun, especially when clarity is helpful.

ponerme would mean to put on myself or to put something on myself, so it does not fit here.

Yes, both can be possible, but they are slightly different in feel.

• sobre = on / on top of
• en = often in / on / at, depending on context

Here:

• sobre el alféizar emphasizes the idea of placing the cactus on top of the windowsill
• en el alféizar can also be natural in Spanish, especially in everyday speech, for something located on the windowsill

So sobre is a bit more literally spatial: resting on the surface.

Alféizar means windowsill.

It refers to the flat ledge at the bottom of a window, inside or outside, where you might place a plant.

It is a useful word, but not one beginners see very early, so it often stands out in a sentence like this.

A sentence can mention both a balcony and a windowsill because they are different things.

• balcón = balcony
• alféizar = windowsill

The stool is left next to the balcony, and the purpose is to put the cactus on the windowsill. The exact physical scene may not be perfectly realistic in every house, but grammatically it is fine.

Also, in Spanish, balcón can sometimes refer to a large window or balcony-style opening, depending on the architecture. So the sentence is not necessarily strange.

Because poner is a verb that takes something that gets placed somewhere.

In:

• poner el cactus sobre el alféizar

the thing being placed is el cactus, so that is the direct object.

The place where it is placed is:

• sobre el alféizar

So the structure is:

• poner = verb
• el cactus = direct object
• sobre el alféizar = location/complement

The same pattern appears earlier:

• Dejé el taburete junto al balcón
• el taburete is the direct object of dejé
• junto al balcón tells you where

Spanish often prefers a full noun where English might use a pronoun, especially if the noun helps keep the sentence clear.

So instead of:

• Dejélo... or para ponerlo...

the sentence uses:

• Dejé el taburete...
• para poner el cactus...

This is very natural. Spanish does use object pronouns, but it does not have to use them as often as English does.

For example, after context is established, you could say:

• Lo dejé junto al balcón para ponerlo sobre el alféizar

But that version is less clear, because lo could refer to either object unless the context helps.

The stressed syllables are:

• de-JÉ
• bal-CÓN
• al-féi-ZAR

Accent marks are written when Spanish spelling rules require them.

• dejé has an accent because it ends in a vowel and the stress is on the last syllable
• balcón has an accent because it ends in n and the stress is on the last syllable
• alféizar has an accent because the written stress falls where it would not normally be expected

These accent marks are important because they show pronunciation and can sometimes distinguish forms.

Yes, somewhat, but the original order is the most neutral and natural.

Original:

• Dejé el taburete junto al balcón para poner el cactus sobre el alféizar.

Other possible word orders include:

• Para poner el cactus sobre el alféizar, dejé el taburete junto al balcón.
• Dejé junto al balcón el taburete para poner el cactus sobre el alféizar.

These are grammatical, but the original sounds the most straightforward in normal speech.

Spanish word order is more flexible than English, but not random. The usual order here is:

• verb
• direct object
• place
• purpose

Possibly, depending on the exact object and the variety of Spanish.

• taburete = stool, very standard
• banqueta can also mean stool or small bench in some varieties, but usage varies by region
• taburetecito is a diminutive, meaning something like little stool

Since the sentence is for Spanish from Spain, taburete is a very natural choice.

The diminutive taburetecito would add a tone of smallness or affection, not just neutral description.