La tapeto estas sub la plafono.

La is the Esperanto definite article, the equivalent of the in English.

It appears before both nouns because the sentence is talking about specific things:

• la tapeto = the wallpaper
• la plafono = the ceiling

A useful point for learners: la never changes. It stays la for singular, plural, and all genders.

In Esperanto, nouns normally end in -o.

So:

• tapeto is a noun
• plafono is a noun

This is one of the most regular parts of Esperanto grammar. If you see a word ending in -o, it is usually a noun.

Not in this case.

Although Esperanto does have a real diminutive suffix -et-, not every sequence of letters e-t inside a word is a suffix. In tapeto, the root is learned as tapet-, and then -o is the noun ending.

So you should treat tapeto as a whole vocabulary item, not as tap- + -et- + -o.

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

So:

• esti = to be
• estas = is / are / am

In Esperanto, present-tense verbs end in -as.
That means estas works for all persons:

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

In this sentence, La tapeto estas sub la plafono literally uses is to link the subject to its location.

Because this sentence describes a location, not movement.

• sub la plafono = under the ceiling
• sub la plafonon would suggest movement toward a position under the ceiling

In Esperanto, a prepositional phrase often takes -n only when direction or motion is being emphasized.

So here:

• La tapeto estas sub la plafono. = The wallpaper is under the ceiling.
  Static location.

Compare with a movement idea:

• La kato saltis sub la tablon. = The cat jumped under the table.
  Movement to that place.

Yes, Esperanto word order is fairly flexible.

The basic order here is:

• La tapeto = subject
• estas = verb
• sub la plafono = location

This is the most straightforward and neutral version.

But other orders can also be grammatical, for example:

• Sub la plafono estas la tapeto.

That puts more emphasis on the location. Even though word order can move around, the original sentence is the clearest and most ordinary for a beginner.

No. Esperanto nouns do not have grammatical gender the way nouns do in languages like French, German, or Spanish.

So:

• tapeto is just a noun
• plafono is just a noun

There is no need to memorize them as masculine, feminine, or neuter.

It is grammatically correct, but it may sound a little unusual depending on context.

The sentence only says that the wallpaper is below the ceiling. That is true in a general spatial sense, but wallpaper is normally thought of as being on the wall, not simply under the ceiling.

So if someone wanted to be more explicit, they might say something like:

• La tapeto estas sur la muro, sub la plafono.
  The wallpaper is on the wall, below the ceiling.

Still, as a simple example sentence for practicing grammar and prepositions, La tapeto estas sub la plafono is perfectly fine.