La broĉo estas el arĝento kaj latuno.

La is the definite article, meaning the.

So la broĉo = the brooch.

If you just say broĉo, it can mean a brooch or brooch in a more general sense, depending on context. Esperanto does not have a separate word for a/an.

Estas is the present-tense form of esti, which means to be.

So:

• mi estas = I am
• vi estas = you are
• ĝi estas = it is

Unlike English, Esperanto uses the same present-tense form estas for all persons.

Here el means out of / made of.

So estas el arĝento kaj latuno means the brooch is made from those materials.

This is a very common use of el:

• taso el vitro = a cup made of glass
• tablo el ligno = a table made of wood

So in this sentence, el tells you what material the brooch consists of.

Because in Esperanto, names of materials and substances are usually nouns:

• arĝento = silver
• latuno = brass
• oro = gold
• ligno = wood

After el, Esperanto normally uses the noun for the material:

• el arĝento
• el latuno
• el ligno

You can also make adjectives from these:

• arĝenta = silver, silvery
• latuna = brass, made of brass

But in this sentence, the noun form after el is the most natural choice.

Because the sentence is talking about the materials in a general sense, not about some specific silver or specific brass already identified in the conversation.

In Esperanto, material words often appear without la when used generally:

• el oro = made of gold
• el ŝtono = made of stone

If you said la arĝento, that would usually mean the silver in some specific context.

Kaj means and.

So:

• arĝento kaj latuno = silver and brass

It is the normal word used to join words, phrases, or clauses.

Because there is no direct object here.

• La broĉo is the subject.
• estas is the verb.
• el arĝento kaj latuno is a prepositional phrase.

Also, nouns after a preposition like el normally do not take -n.

So arĝento and latuno stay as they are.

A few useful points:

• ĉ sounds like ch in church
• ĝ sounds like j in judge
• stress in Esperanto is always on the second-to-last syllable

So:

• broĉo is pronounced roughly BRO-cho
• arĝento is pronounced roughly ar-JEN-to
• latuno is pronounced roughly la-TU-no

That fixed stress pattern is very helpful in Esperanto.

Yes, that is possible, but it is a little different in feel.

• La broĉo estas el arĝento kaj latuno focuses clearly on the materials it is made from.
• La broĉo estas arĝenta kaj latuna uses adjectives, so it describes the brooch as silver and brass in quality or material.

In many contexts both are understandable, but el + material noun is especially clear when you mean actual composition.