Она прочитала длинное послание.

Прочитала is the perfective past form of прочитать, so it presents the action as completed: she finished reading the message.

By contrast, читала is the imperfective past form of читать, which would usually mean she was reading, used to read, or simply focuses on the process rather than the result.

So:

• Она читала длинное послание. = She was reading / she read (process-focused)
• Она прочитала длинное послание. = She read the whole message / finished reading it

In the past tense, Russian verbs are formed from the past stem plus endings that show gender and number.

Because the subject is она (she), the verb takes the feminine singular past ending:

• masculine: прочитал
• feminine: прочитала
• neuter: прочитало
• plural: прочитали

So она прочитала means she read.

Длинное is the adjective длинный (long) agreeing with послание.

Russian adjectives must agree with the noun in:

• gender
• number
• case

Here, послание is:

• neuter
• singular
• accusative

Because it is an inanimate noun, its accusative form is the same as the nominative. So the adjective also takes the neuter singular accusative/nominative form:

• длинный = masculine
• длинная = feminine
• длинное = neuter
• длинные = plural

Послание is a neuter singular inanimate noun. In this sentence it is the direct object of the verb, so it is in the accusative case.

For most inanimate Russian nouns, the accusative singular looks the same as the nominative singular. So:

• nominative: послание
• accusative: послание

That is why the word does not visibly change here.

A very common clue is the ending -ие / -е. Many nouns ending this way are neuter.

So послание behaves like a neuter noun:

• интересное послание
• новое послание
• длинное послание

A learner should still remember that Russian gender is not always perfectly predictable, but here the ending is a strong clue.

Not exactly.

Послание often sounds more formal, literary, or elevated than письмо. It can mean message, epistle, or missive, depending on context.

• письмо = a letter, often the normal everyday word
• послание = a message/letter with a more formal, expressive, or literary tone

So this sentence may sound a bit more stylistic than if it used письмо.

Yes, Russian often omits subject pronouns when the subject is clear from context.

So both of these are possible:

• Она прочитала длинное послание.
• Прочитала длинное послание.

Including она can help by:

• making the subject explicit
• creating contrast
• sounding clearer in isolation

In a standalone teaching sentence, keeping она is very natural.

Yes. Russian word order is more flexible than English because case endings show grammatical roles.

The neutral order here is:

• Она прочитала длинное послание.

But other orders are possible:

• Длинное послание она прочитала.
  This emphasizes the long message.
• Она длинное послание прочитала.
  This can sound contrastive or stylistically marked.
• Прочитала она длинное послание.
  This is possible in certain contexts, often with special emphasis.

Even though the order can change, the most basic neutral version is the one you were given.

The usual stress is:

• она́
• прочита́ла
• дли́нное
• посла́ние

So the whole sentence is pronounced:

она́ прочита́ла дли́нное посла́ние

Stress is important in Russian because it is not always predictable and can affect vowel pronunciation.

Russian past tense does not map perfectly onto English tense choices.

Depending on context, она прочитала could be translated as:

• she read
• she has read
• sometimes even she had read in the right context

The form itself mainly tells you:

• it is past
• it is perfective
• the action is seen as completed

The exact English tense depends on the surrounding context.

Russian has no articles like a/an or the.

So длинное послание could mean:

• a long message
• the long message

Context tells you which meaning is intended.

This is very normal in Russian, and learners need to get used to understanding definiteness from the situation rather than from an article.