Поддоны штабелируют рядом со стеллажом.

Not in this sentence.

Here поддоны is the direct object: pallets are what someone is stacking.

Why is that not obvious from the form? Because for inanimate masculine nouns in the plural, the accusative looks exactly like the nominative:

• nominative plural: поддоны
• accusative plural: поддоны

So the form alone does not tell you the role. You understand it from the verb and the overall pattern of the sentence.

A very literal gloss would be:

• Поддоны = pallets
• штабелируют = they stack
• рядом со стеллажом = next to the rack / shelving unit

So literally: They stack pallets next to the rack.

In natural English, this is often translated as Pallets are stacked next to the rack.

This is a very common Russian pattern called an indefinite-personal construction.

Russian often uses a 3rd person plural verb with no subject stated when the exact people doing the action are unimportant, unknown, or obvious from context.

So:

• штабелируют literally means they stack
• but it often really means someone / people / workers stack

In English, we usually prefer a passive translation in this kind of sentence:

• Russian: Поддоны штабелируют...
• natural English: Pallets are stacked...

This is especially common in:

• instructions
• technical writing
• workplace procedures
• descriptions of how things are normally done

It can use passive forms, but Russian often prefers this active-looking 3rd plural construction when the agent is unimportant.

So instead of something that more directly resembles English are stacked, Russian very naturally says the equivalent of:

• They stack pallets...

even when no actual they is meant.

This often sounds more normal and less heavy than a formal passive. So for warehouse, technical, or procedural language, Поддоны штабелируют... is very natural.

рядом с/со means next to, beside, or near.

So:

• рядом со стеллажом = next to the rack / shelving unit

The form со is just a pronunciation-friendly variant of с. Russian often uses со before awkward consonant clusters.

Here the next word is стеллажом, which begins with ст-, so:

• со стеллажом sounds smoother than
• с стеллажом

So this is mostly about ease of pronunciation.

Because рядом с/со requires the instrumental case.

The pattern is:

• рядом с кем? с чем? = next to whom? next to what?

So стеллаж changes to instrumental singular:

• nominative: стеллаж
• instrumental: стеллажом

That is why the sentence has со стеллажом.

Yes, sometimes.

• рядом by itself can mean nearby
• but if you say what something is near to, Russian normally uses с/со + instrumental

Compare:

• Поддоны стоят рядом. = The pallets are nearby.
• Поддоны стоят рядом со стеллажом. = The pallets are next to the rack.

So in your sentence, once the specific reference point is named, со стеллажом is expected.

Yes, a little.

Russian word order is more flexible than English because case endings help show grammatical roles. Putting поддоны first makes pallets the topic of the sentence.

So this order suggests something like:

• As for the pallets, they stack them next to the rack.

It is still natural Russian, especially if the discussion is already about pallets.

A different order could also be possible, for example:

• Рядом со стеллажом штабелируют поддоны.

That version puts a bit more attention on the location first.

So the given order is not strange; it just reflects Russian information structure rather than rigid English-style word order.

штабелируют is imperfective.

The imperfective is used because this sentence describes:

• a general procedure
• a normal practice
• an ongoing process
• how something is done in a workplace setting

It is not focusing on the single completed result of one action. It is more like:

• This is how pallets are stacked
• Pallets get stacked this way / in this place

That is why the imperfective is the natural choice.

It is more specific than that.

штабелировать means to stack, especially in a technical or warehouse sense: to arrange items in a stack or pile.

So it is more precise than broad verbs like:

• класть = put, lay
• ставить = put, stand
• складывать = put together / pile up / stack, depending on context

In a logistics or storage context, штабелировать sounds technical and exact.

You do not know from the Russian noun alone, because Russian has no articles.

So со стеллажом can mean either:

• next to a rack
• next to the rack

Context decides which one is right.

In an isolated sentence, English translators choose whichever sounds most natural for the situation. In a warehouse instruction, the rack is often a reasonable choice if a specific rack is already understood.