sofa no usiro ni neko ga imasu.

Here, の links two nouns together.

• ソファ = sofa
• 後ろ = back / behind
• ソファの後ろ = the back of the sofa / behind the sofa

A very literal way to think of it is the sofa’s back/behind, though in natural English we would usually say behind the sofa.

後ろ means behind or the back.

In Japanese, words like 上 (above), 下 (below), 前 (in front), 後ろ (behind), 中 (inside), and 外 (outside) are often treated like nouns. That is why you often see them in patterns like:

• X の 後ろ = behind X
• X の 前 = in front of X
• X の 上 = on top of X

So ソファの後ろ is literally the area behind the sofa.

に marks the location where something exists in sentences with います or あります.

So in this sentence:

• ソファの後ろに = behind the sofa
• 猫がいます = there is a cat

Together: There is a cat behind the sofa.

This に is not the same as the に used for time or indirect objects, although it is the same particle. Here its job is to mark location.

が marks 猫 as the grammatical subject: a cat is what exists.

In existence sentences, が is very common because it introduces the thing that is there:

• 猫がいます = there is a cat
• 犬がいます = there is a dog

If you said 猫はいます, it would sound more like:

• As for the cat, it is there
• or There is a cat, at least / with some contrast

So が is the most neutral and natural choice here.

Japanese uses different existence verbs depending on whether the thing is animate or inanimate.

• います: for people and animals
• あります: for objects and things

Since 猫 is a living animal, you use います.

Examples:

• 猫がいます。 = There is a cat.
• 本があります。 = There is a book.

The sentence follows a very common Japanese pattern:

[place] に [thing] が います

So here:

• ソファの後ろに = in the location behind the sofa
• 猫が = a cat
• います = exists / is

A very literal order would be:

Behind the sofa, a cat exists.

Natural English: There is a cat behind the sofa.

Japanese verbs normally come at the end, so います must go last.

後ろ is read うしろ.

So the full sentence is read:

ソファ の うしろ に ねこ が います。

Notes:

• 猫 = ねこ
• 後ろ = うしろ

Yes, there can be, depending on context, but this sentence itself does not explicitly state one with は.

Japanese often leaves out information that is already understood. So in conversation, this sentence could simply be giving new information:

• ソファの後ろに猫がいます。
• There’s a cat behind the sofa.

If you wanted to make the location the topic, you could say:

• ソファの後ろには猫がいます。

That can sound more contrastive, like As for behind the sofa, there is a cat there.

The spaces are just for learners. Normal Japanese writing usually does not use spaces between words.

So this learner-friendly version:

ソファ の 後ろ に 猫 が います。

would normally be written as:

ソファの後ろに猫がいます。

In some contexts, yes, but the most neutral reading is There is a cat behind the sofa.

Because of 猫がいます, the sentence focuses on the existence of a cat in that location. If you specifically meant The cat is behind the sofa, you might more naturally use a sentence where the cat is the topic:

• 猫はソファの後ろにいます。

That means The cat is behind the sofa or As for the cat, it is behind the sofa.

So the original sentence is more like introducing the cat’s presence, not talking about a specific already-known cat.

No, に is the correct particle here.

With います and あります, the location of existence is marked by に:

• 公園に犬がいます。 = There is a dog in the park.

で marks the place where an action happens, not where something simply exists:

• 公園で遊びます。 = I play in the park.

Since いる is an existence verb, not an action like play, you use に, not で.