Собранный шкаф стоит у стены.

Собранный is a full past passive participle from the verb собрать. In practice, it behaves a lot like an adjective and describes the noun шкаф.

So in собранный шкаф, it means something like assembled or put together, but grammatically it is still related to the verb собрать.

Yes, very close.

Собранный шкаф is a more compact participial way to say:

• шкаф, который собрали
• or шкаф, который был собран

So Russian often uses a participle where English might use:

• the wardrobe that was assembled
• the assembled wardrobe

Because собранный is the full form, which is used before a noun as a modifier:

• собранный шкаф = the assembled wardrobe

The short form собран is usually used as part of the predicate:

• Шкаф собран. = The wardrobe is assembled.

So:

• собранный шкаф = attributive use
• шкаф собран = predicative use

Because it agrees with шкаф, which is:

• masculine
• singular
• nominative

Russian adjectives and participles must agree with the noun they describe.

Here are matching forms:

• собранный шкаф — masculine singular
• собранная тумба — feminine singular
• собранное кресло — neuter singular
• собранные стулья — plural

Because шкаф is the subject of the sentence.

The thing doing the action of standing is the wardrobe, so Russian uses the nominative:

• шкаф стоит

That is the basic subject + verb structure.

Стоит is the 3rd person singular of стоять, meaning to stand.

Russian often uses position verbs with objects:

• стоять = stand
• лежать = lie
• сидеть = sit

So шкаф стоит literally means the wardrobe stands or is standing. For a tall upright object like a wardrobe, стоять is the natural choice.

Russian usually does not use the present-tense form of to be the way English does.

Also, in this sentence, the main verb is already стоит, so Russian does not need a separate word for is.

Compare:

• Шкаф стоит у стены. = The wardrobe is standing by the wall.
• Шкаф у стены. = The wardrobe is by the wall.
  (very natural too, with no verb)

So the sentence is not missing anything.

Because the preposition у requires the genitive case.

The dictionary form is стена, but after у it becomes стены:

• стена → nominative singular
• стены → genitive singular

So:

• у стены = by the wall / next to the wall

Here у means by, next to, or near.

It does not literally mean at in the same way as English at, and it does not mean on. It shows proximity:

• у стены = by the wall
• у окна = by the window
• у двери = by the door

So it marks location near something.

Because собранный is just a normal modifier directly attached to the noun:

• собранный шкаф

A single participle before the noun is not separated by commas.

You may see commas with a longer participial phrase, especially after the noun, for example:

• Шкаф, собранный вчера, стоит у стены.

There the participial phrase is more detached, so commas are used.

Yes. Russian word order is flexible, and changing it usually changes focus, not the basic meaning.

For example:

• Собранный шкаф стоит у стены. — neutral
• У стены стоит собранный шкаф. — emphasizes the location
• Шкаф стоит у стены. — leaves out собранный
• Стоит у стены собранный шкаф. — more literary or marked

So the original sentence is a normal, neutral way to say it.

Because Russian has no articles.

So шкаф can mean:

• a wardrobe
• the wardrobe

The exact meaning depends on context.

In this sentence, English needs an article, but Russian does not.