En el escaparate de la pastelería había una tarta muy grande con fresas y chocolate.

Because haber in había is being used in its existential sense: there was / there were.

So:

• Había una tarta... = There was a cake...

By contrast, estaba would describe the location or state of something already identified:

• La tarta estaba en el escaparate. = The cake was in the shop window.

A useful shortcut:

• había = there was / there were
• estaba / estaban = was / were for something specific

In this sentence, the speaker is introducing the cake as something that existed in that place, so había is the natural choice.

Because in this use, haber stays in the singular.

So Spanish says:

• Había una tarta. = There was one cake.
• Había dos tartas. = There were two cakes.

Even with a plural noun, standard Spanish normally keeps haber singular in existential sentences.

So:

• correct: Había muchas tartas
• non-standard in careful Spanish: Habían muchas tartas

This is a very common point for learners because English changes was/were, but Spanish usually does not here.

En means in / on / at, depending on context. Here en el escaparate means in the shop window / in the display window.

Escaparate in Spain usually refers to the window display at the front of a shop. So the cake is being described as being visible there.

Examples:

• en el escaparate = in the shop window
• en la mesa = on the table
• en la tienda = in the shop

Spanish often uses en where English may choose different prepositions.

In Spain, escaparate usually means shop window or display window: the glass front display where shops present products.

So:

• el escaparate de la pastelería = the pastry shop's window display

Depending on context, English might translate it as:

• shop window
• display window
• store window

In some other Spanish-speaking regions, you may also hear words like vitrina, but escaparate is very common in Spain.

De la pastelería means of the pastry shop or more naturally in English, the pastry shop's.

So:

• el escaparate de la pastelería = the pastry shop window

This is a very common Spanish structure:

• la puerta de la casa = the door of the house / the house door
• el dueño del restaurante = the owner of the restaurant

Spanish often uses de where English might use apostrophe 's or a noun used adjectivally.

Pastelería is a pastry shop or cake shop. It focuses on cakes, pastries, sweets, and similar items.

It is not always exactly the same as bakery in English.

Compare:

• pastelería = pastry shop / cake shop
• panadería = bakery / bread shop

Some places can function as both, but the word pastelería specifically suggests pastries, cakes, desserts, and sweets.

Because una tarta introduces the cake as new information: a cake, not the cake.

• una tarta = a cake
• la tarta = the cake

Since the cake has not been mentioned before, Spanish uses the indefinite article una.

If both speaker and listener already knew which cake was being talked about, you could say:

• En el escaparate de la pastelería estaba la tarta que habíamos encargado.

But in the original sentence, it is just introducing one cake among possible others.

In Spanish, adjectives usually come after the noun.

So:

• una tarta grande = a big cake
• una casa bonita = a pretty house

That is the normal pattern.

Here, muy grande simply means very big:

• una tarta muy grande = a very big cake

Sometimes adjectives can go before the noun, but that often changes the tone or emphasis. For everyday description, tarta grande is the standard order.

Because muy is used to modify adjectives and adverbs, while mucho is used mainly with nouns or as a pronoun/adverb in other contexts.

Here grande is an adjective, so you need:

• muy grande = very big

Compare:

• muy grande = very big
• mucho chocolate = a lot of chocolate

So:

• correct: una tarta muy grande
• not correct here: una tarta mucho grande

By itself, con fresas y chocolate simply means with strawberries and chocolate.

It can suggest:

• decorated with strawberries and chocolate
• topped with strawberries and chocolate
• made with strawberries and chocolate

The exact meaning depends on context. In a sentence about a cake in a shop window, many people would naturally picture a cake decorated or covered with strawberries and chocolate.

Spanish often leaves that kind of detail unstated unless it matters.

That is a very natural word order in Spanish when presenting something that exists somewhere.

The structure is:

• En + place + había + thing

So:

• En el jardín había un perro.
• En la mesa había dos vasos.
• En el escaparate de la pastelería había una tarta...

This feels natural because the sentence first sets the scene, then says what was there.

You could also say:

• Había una tarta muy grande con fresas y chocolate en el escaparate de la pastelería.

That is also grammatical, but the original order sounds especially good if you want to focus first on the location.

Había is the imperfect of haber, and it is often used to describe a scene or background in the past.

Here the sentence is painting a picture:

• in the pastry shop window, there was a very large cake...

That is descriptive, so había fits well.

Hubo is the preterite, and it usually sounds more like a completed event or occurrence:

• Hubo un accidente. = There was an accident.
• Hubo un problema. = There was a problem.

For describing what was visible in a setting, había is much more natural.

Yes. This is exactly one of the main uses of había:

• había = there was / there were

Even though English uses there was, Spanish does not use a separate word for that there. The idea is built into haber.

So:

• Había una tarta = There was a cake
• Había muchas tartas = There were many cakes

This is one of the most important meanings of haber to learn.

Yes, they are important. They are part of the correct spelling and pronunciation.

• había
• pastelería

The written accent shows which syllable is stressed.

Very roughly:

• ha-BÍ-a
• pas-te-le-RÍ-a

Without the accent marks, the words would be misspelled and could suggest the wrong pronunciation. In Spanish, accents are not optional decorations; they are a normal part of the language.

It is understandable, but it is less natural in this context.

Why?

Because estar usually works better when you are locating something specific or already known:

• La tarta estaba en el escaparate.

But when you are introducing something as existing in a place, Spanish prefers haber:

• En el escaparate había una tarta...

So the original sentence sounds more natural because it is presenting the cake as part of the scene, not locating a previously identified cake.