La pasta cerámica está en el molde.

Because Spanish uses estar for location. If you are saying where something is, estar is the usual verb.

• La pasta cerámica está en el molde = the ceramic paste is in the mould.
• Es would be used more for identity or classification:
  • Es pasta cerámica = it is ceramic paste.

So here, the important idea is location, not identity.

Because pasta is a feminine singular noun, so it takes la, and molde is a masculine singular noun, so it takes el.

• la pasta
• el molde

Spanish uses articles very often, especially when referring to specific things. In this sentence, we are talking about a particular ceramic paste and a particular mould.

Because adjectives in Spanish must agree with the noun they describe.

Here, cerámica describes pasta, and pasta is feminine singular, so the adjective must also be feminine singular:

• pasta cerámica

If the noun were masculine, you would use cerámico instead:

• material cerámico

In Spanish, descriptive adjectives usually come after the noun. So pasta cerámica is the normal order.

This is one of the big differences from English, where adjectives usually come before the noun. English says ceramic paste, but Spanish normally says pasta cerámica.

Not necessarily. In Spanish, pasta can have several meanings depending on context. It can refer to food, but it can also mean paste, dough, or a soft workable material.

In a ceramics context, pasta cerámica refers to ceramic paste or clay-like material, not noodles.

Because en is the normal preposition for expressing location in many cases. Here it means in:

• en el molde = in the mould

If you wanted to stress that something is physically inside, you could also say dentro del molde, but en el molde is perfectly natural and more neutral.

Yes. Spanish often leaves out the subject if it is already clear from the context.

So if everyone already knows you are talking about the ceramic paste, you can simply say:

• Está en el molde = It is in the mould.

But if you want to state the subject clearly, especially when introducing it, you keep La pasta cerámica.

Yes, Spanish word order is more flexible than English word order.

The most neutral version is:

• La pasta cerámica está en el molde.

But you could also say:

• En el molde está la pasta cerámica.

That version sounds more emphatic or literary, as if you are highlighting the location. For normal use, the original order is the safest choice.

The accent mark shows the correct stress: es-TÁ.

It is part of the standard spelling of that verb form. It also helps distinguish está from esta in writing.

So:

• está = is
• esta = this / this one

You would change the articles, adjective, verb, and nouns as needed:

• Las pastas cerámicas están en los moldes.

Notice the changes:

• la → las
• cerámica → cerámicas
• está → están
• el → los
• molde → moldes

This is a good example of how several words in a Spanish sentence often change together to match number and gender.