La farmacia está a un kilómetro de mi casa.

Spanish uses estar for location.

• La farmacia está... = the pharmacy is located...
• Ser is usually for identity, definition, origin, etc.
• Estar is usually for location and temporary states.

So when you say where something is, estar is the normal verb:

• La farmacia está cerca.
• Mi casa está en Madrid.

Here a means something like at a distance of or away by.

So:

• está a un kilómetro de mi casa = it is one kilometre from my house

This is a very common Spanish pattern for distance:

• Está a dos minutos.
• Estamos a 5 km del centro.
• El hotel está a media hora de aquí.

English does not use at in the same way here, so this often feels unusual to learners.

Because uno changes before a masculine singular noun.

• uno becomes un before a masculine singular noun
• una is used before a feminine singular noun

Since kilómetro is masculine, you say:

• un kilómetro

Compare:

• un libro
• un coche
• una casa
• una farmacia

So uno kilómetro is not correct.

De here means from.

So the structure is:

• a un kilómetro de... = one kilometre from...

Examples:

• La estación está a un kilómetro del hotel.
• El colegio está a dos calles de aquí.

So de mi casa simply means from my house.

Because Spanish usually uses the definite article with specific nouns more often than English does.

• La farmacia = the pharmacy

If you are talking about a particular pharmacy, la is natural.

Also, farmacia is a feminine noun, so it takes the feminine article:

• la farmacia
• una farmacia

You cannot say el farmacia because the noun is feminine.

In standard modern Spanish, possessives like mi, tu, su, nuestro normally replace the article.

So you say:

• mi casa
• tu coche
• su farmacia

Not:

• la mi casa
• el tu coche

So de mi casa is the normal form.

The accent mark shows the correct stress and also helps distinguish forms.

• está = he/she/it is or you are from estar
• esta without an accent usually means this (feminine)

Examples:

• Esta farmacia = this pharmacy
• La farmacia está lejos = the pharmacy is far away

So the accent is important.

Because the stress falls on the second syllable:

• ki-LÓ-me-tro

Spanish spelling rules require a written accent here.

This is useful because stress in Spanish is very regular, and accent marks tell you when a word does not follow the default pattern.

Yes, a little.

The most neutral order is:

• La farmacia está a un kilómetro de mi casa.

But Spanish can move parts around for emphasis:

• A un kilómetro de mi casa está la farmacia.

That version sounds more marked or literary, and it emphasizes the distance/location first.

For everyday speech, the original sentence is the most natural.

Yes. In many contexts, quedar can also be used to talk about where a place is located.

• La farmacia está a un kilómetro de mi casa.
• La farmacia queda a un kilómetro de mi casa.

Both are understandable.
Está is more basic and universally useful for learners, so it is usually the safest choice.

You could ask:

• ¿La farmacia está a un kilómetro de mi casa? = Is the pharmacy one kilometre from my house?

Or, more naturally if you want to ask about distance:

• ¿A qué distancia está la farmacia de mi casa? = How far is the pharmacy from my house?

Useful related questions:

• ¿Está lejos la farmacia? = Is the pharmacy far?
• ¿Está cerca de mi casa? = Is it near my house?

You keep the same structure:

• La farmacia está a dos kilómetros de mi casa.
• La farmacia está a medio kilómetro de mi casa.
• La farmacia está a diez minutos de mi casa.

So the pattern is:

[place] + está + a + distance/time + de + [reference point]

This structure works with physical distance and also very often with travel time.

Usually yes in this kind of sentence: farmacia is the place where you get medicines.

A small cultural note: in Spain, a farmacia is specifically a pharmacy, not a general convenience store or supermarket drugstore section. So the word is fairly precise.

In this sentence, though, you can simply understand it as pharmacy.