La moderna kolektejo estas granda.

In Esperanto, adjectives end in -a. So moderna means modern as an adjective describing a noun.

Here, moderna describes kolektejo, so it takes the adjective ending -a.

Because granda is still an adjective.

In La moderna kolektejo estas granda, the word granda describes the subject kolektejo after the verb estas. This is called a predicate adjective in English grammar.

Esperanto keeps the adjective ending -a whether the adjective comes before the noun or after estas:

• granda domo = a big house
• la domo estas granda = the house is big

Kolektejo is made from parts:

• kolekt- = the idea of collecting
• -ej- = place for something
• -o = noun ending

So kolektejo means something like a place for collecting, collection place, depot, or collection center, depending on context.

This is a very common pattern in Esperanto. For example:

• lerni = to learn
• lernejo = school, literally place for learning

-ej- is a very common Esperanto suffix meaning place associated with an action or purpose.

Examples:

• kuiri = to cook → kuirejo = kitchen
• dormi = to sleep → dormejo = dormitory / sleeping place
• vendi = to sell → vendejo = shop / place of selling

So in kolektejo, -ej- tells you this is a place connected with collecting.

La is the definite article, meaning the.

Esperanto has only one article:

• la = the

It does not have a separate word for a or an. So:

• kolektejo can mean a collection place or just collection place
• la kolektejo means the collection place

Estas is the present tense of esti, meaning to be.

So:

• mi estas = I am
• vi estas = you are
• li estas = he is
• ĝi estas = it is
• ili estas = they are

Unlike English, the verb does not change depending on the subject. That makes Esperanto verbs much simpler.

Because there is no direct object here.

The sentence has:

• a subject: La moderna kolektejo
• a linking verb: estas
• a predicate adjective: granda

The -n ending is mainly used for a direct object or for motion toward something. Neither of those is happening here.

So this sentence stays:

• La moderna kolektejo estas granda.

not

• La modernan kolektejon estas grandan. ❌

Yes. In Esperanto, adjectives agree with the nouns they describe in number and case.

Here the noun is singular and has no -n, so the adjectives are also singular and have no -n:

• la moderna kolektejo
• granda

If the noun were plural, the adjectives would also become plural:

• La modernaj kolektejoj estas grandaj.
  = The modern collection places are big.

Esperanto word order is fairly flexible, but this sentence uses the most normal and straightforward order:

• La moderna kolektejo = subject
• estas = verb
• granda = complement

So this is the standard pattern:

The modern collection place is big.

Because Esperanto marks word roles clearly, some variation is possible, but this normal order is best for learners.

They are doing two different jobs:

• moderna directly modifies the noun: the modern collection place
• granda comes after estas and tells what the subject is like: is big

So:

• la moderna kolektejo = noun phrase
• estas granda = statement about that noun phrase

This works similarly to English:

• the modern building
• the building is big

A simple pronunciation guide is:

la mo-DER-na ko-lek-TE-jo ES-tas GRAN-da

A few useful points:

• Stress in Esperanto is almost always on the second-to-last syllable
• j sounds like English y
• e is like e in met
• o is a clear o

So kolektejo sounds roughly like ko-lek-TAY-yo.

Yes. The exact English translation depends on context.

Because kolektejo literally means place for collecting, it could be translated as:

• collection center
• collection point
• depot
• storage place
• collection facility

So the Esperanto grammar is clear, but the best English wording can vary depending on what kind of place is meant.

Yes. It is a complete sentence with all the basic parts needed:

• La moderna kolektejo = subject
• estas = verb
• granda = complement

So grammatically it is a full, normal Esperanto sentence.