Kolekti monon estas la ĉefa celo.

The ending -i marks the infinitive in Esperanto, like to collect in English.

In this sentence, kolekti is being used as the subject of the sentence:

• Kolekti monon = collecting money / to collect money

Esperanto often uses the infinitive this way, so a verb can act like a noun phrase.

The -n shows the direct object.

Here, mono is the thing being collected, so it becomes:

• mono = money
• monon = money as the direct object

So:

• kolekti monon = to collect money

This is very typical in Esperanto: the thing directly affected by the verb gets -n.

Because money is usually treated as a general, uncountable idea here.

So:

• mono = money in general
• monoj = monies, sums of money, or different kinds of money

In most ordinary sentences, monon is the natural choice.

La is the definite article, meaning the.

So:

• ĉefa celo = a main goal / main goal
• la ĉefa celo = the main goal

Using la shows that we are talking about a specific, identifiable goal, not just any goal.

Because ĉefa is an adjective, and Esperanto adjectives end in -a.

So:

• ĉefa = main, chief
• celo = goal

Together:

• ĉefa celo = main goal

This is one of the most regular parts of Esperanto grammar:

• nouns end in -o
• adjectives end in -a

Because ĉefa belongs to celo, not to monon.

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

Here:

• ĉefa describes celo
• celo is not a direct object
• so neither word gets -n

If celo were in the accusative, then ĉefa would also take -n:

• la ĉefan celon

But in this sentence, that is not needed.

Yes. The whole infinitive phrase kolekti monon acts as the subject.

So the structure is:

• Kolekti monon = subject
• estas = is
• la ĉefa celo = predicate/complement

This is similar to English:

• Collecting money is the main goal.

Yes, absolutely.

Both are grammatical:

• Kolekti monon estas la ĉefa celo.
• La ĉefa celo estas kolekti monon.

The difference is mostly one of focus or style:

• starting with Kolekti monon emphasizes the action
• starting with La ĉefa celo emphasizes the goal itself

Esperanto word order is fairly flexible because endings show the grammar clearly.

Because kolekti monon is not expressing purpose here. It is the subject.

Compare:

• Kolekti monon estas la ĉefa celo.
  = Collecting money is the main goal.

• La ĉefa celo estas por kolekti monon.
  This is less natural in standard Esperanto for this meaning.

If you want to express purpose, Esperanto often uses:

• La ĉefa celo estas kolekti monon.
• or a clause such as ... por ke ...

So in this sentence, no por is needed.

Yes. Esperanto verbs do not change according to person or number.

So:

• mi estas = I am
• li estas = he is
• ili estas = they are
• kolekti monon estas = collecting money is

This is much simpler than English, where verbs can change form.

Yes, but the meaning becomes slightly more noun-like.

Compare:

• kolekti monon = to collect money / collecting money
• kolektado de mono = the collecting of money / money-collecting

The version with -ado sounds more like the process or activity itself as a noun.

So:

• Kolekti monon estas la ĉefa celo. = very natural
• Kolektado de mono estas la ĉefa celo. = also possible, a bit more abstract or formal

The letter ĉ is pronounced like ch in church.

So:

• ĉefa sounds roughly like CHEH-fa

Also, Esperanto stress normally falls on the second-to-last syllable:

• ko-LEK-ti
• mo-NON
• ES-tas
• ĈE-fa
• CE-lo

So the whole sentence is pronounced roughly:

• ko-LEK-ti mo-NON ES-tas la ĈE-fa CE-lo

Because Esperanto does not use la unless the noun is specifically definite.

Here, money is meant in a general sense, so monon is enough.

Compare:

• kolekti monon = collect money
• kolekti la monon = collect the money

The second one would mean some specific money already known from context.