Сопроводительный документ помогает декларировать товар.

Сопроводительный means accompanying, supporting, or shipping-related, depending on context.
So сопроводительный документ is an accompanying document or supporting document.

In trade, customs, or shipping contexts, it often refers to paperwork that goes together with the goods.

Because документ is a masculine noun.

The adjective must agree with the noun in gender, number, and case:

• сопроводительный = masculine singular
• документ = masculine singular

If the noun were neuter, you would use сопроводительное.
For example:

• сопроводительное письмо = an accompanying letter

Because it is the subject of the sentence — the thing performing the action.

In Сопроводительный документ помогает декларировать товар, the document is what helps, so it appears in the nominative:

• сопроводительный документ = the accompanying document

Помогает is the 3rd person singular present tense form of помогать.

Here is the logic:

• dictionary form: помогать = to help
• subject: документ = document
• документ is singular
• therefore: документ помогает = the document helps

This is the normal present-tense agreement pattern.

Because after помогать, Russian often uses an infinitive to show what action is being helped.

So:

• помогает = helps
• декларировать = to declare
• помогает декларировать = helps declare / helps to declare

This is very natural Russian syntax.

Because товар is the direct object of декларировать.

You declare what?
You declare товар.

So it must be in the accusative.

For this noun, the accusative looks the same as the nominative because:

• товар is masculine
• it is inanimate

For many masculine inanimate nouns, nominative and accusative are identical:

• nominative: товар
• accusative: товар

Yes. In commercial Russian, товар is often used as a general or collective noun and can correspond to English goods or merchandise, even though it is grammatically singular.

So depending on context, декларировать товар may mean:

• declare the goods
• declare the merchandise
• declare the item/product

Russian often uses singular where English may prefer a plural or collective expression.

It can be used in more than one pattern.

A very common pattern is:

• помогать + dative = to help someone

Example:

• Я помогаю другу. = I help my friend.

But Russian also commonly uses:

• помогать + infinitive = to help do something

Example:

• Этот документ помогает оформить груз. = This document helps process the cargo.

In your sentence, the focus is on the action being helped, so the infinitive pattern is used.

Yes. Russian word order is fairly flexible.

The neutral order here is:

• Сопроводительный документ помогает декларировать товар.

But other orders are possible for emphasis, for example:

• Товар помогает декларировать сопроводительный документ.
  This sounds marked and emphasizes товар.

Even though the order can change, the cases still show the grammatical roles.
That said, the original version is the most natural neutral wording.

Декларировать is imperfective.

Here it is used because the sentence describes a general function or process:

• the document helps with declaring goods

Russian often uses the imperfective infinitive after verbs like help, especially when speaking about a general activity rather than one completed result.

A perfective alternative such as задекларировать would focus more on successfully declaring something as a completed act, which is less natural in this kind of general statement.

No. Russian does not use a separate word corresponding to English to before the infinitive in this structure.

The infinitive itself already means to declare:

• декларировать = to declare

So:

• помогает декларировать товар

literally works as helps declare goods or helps to declare goods.

The main stresses are:

• сопроводи́тельный
• докуме́нт
• помога́ет
• деклари́ровать
• това́р

A rough pronunciation guide:

• sapravadEETyel-nyy dakooMYENT pamaGAyet dyeklariROvat tavaR

The stress is important in Russian, especially in longer words like сопроводи́тельный and деклари́ровать.

Yes. That is a very natural English rendering.

Depending on context, you could translate it as:

• The accompanying document helps declare the goods.
• The accompanying document helps with declaring the goods.
• The supporting document helps with customs declaration of the goods.

The best translation depends on how technical or natural you want the English to sound.