Мы шли сквозь лес.

Шли is the past tense plural of идти, which means to go / be going in one direction, as a process.

So Мы шли сквозь лес means We were walking / going through the forest.

Why not the others?

• ходили (from ходить) usually suggests repeated movement, movement in various directions, or a completed trip there and back.
• пошли means set off / started going, so it focuses on the beginning of the movement.

Compare:

• Мы шли сквозь лес. = We were going through the forest.
• Мы пошли сквозь лес. = We set off through the forest.
• Мы ходили через лес. = We used to go through the forest / we went through the forest and back / on different occasions, depending on context.

So шли is the natural choice for describing ongoing movement in a specific direction.

Yes, Russian can often omit subject pronouns when they are clear from the verb form.

So both of these are possible:

• Мы шли сквозь лес.
• Шли сквозь лес.

Because шли is plural past tense, the sentence already suggests we or they, and context usually tells you which one is meant.

Including мы makes the subject explicit. It can be used:

• for clarity,
• for emphasis,
• or simply because the speaker chooses to say it.

So мы is not grammatically required here, but it is completely normal.

In the past tense, Russian verbs agree with the subject in gender and number.

For идти in the past tense:

• я шёл / я шла = I went / was going
• он шёл = he went / was going
• она шла = she went / was going
• оно шло = it went / was going
• мы шли = we went / were going
• они шли = they went / were going

The ending -и marks the plural past form.

So because мы is plural, the verb must be шли.

After сквозь, the noun is normally in the accusative case.

So in сквозь лес, лес is accusative.

However, for an inanimate masculine noun like лес, the accusative singular has the same form as the nominative singular:

• nominative: лес
• accusative: лес

That is why the form does not change.

If the noun were different, you might see the case more clearly. For example:

• сквозь чащу = through the thicket
  Here чаща changes to чащу in the accusative.

Сквозь means through, often with a sense of passing within or across something that surrounds, contains, or obstructs you.

In Мы шли сквозь лес, it gives the image of moving through the forest itself, among the trees.

It is similar to через, but not always identical.

Very roughly:

• через = through / across
• сквозь = through, often with a stronger sense of penetrating or passing within something

Compare:

• идти через дорогу = to go across the road
• идти сквозь лес = to go through the forest
• свет сквозь окно = light through the window
• смотреть сквозь стекло = to look through glass

In many contexts, both may be possible, but сквозь лес sounds especially natural when you imagine moving among the trees.

It can mean either, depending on context.

Russian does not have a separate past progressive form like English were walking. Instead, the imperfective verb шли can express:

• an ongoing action in the past: we were walking
• a simple past event seen as a process: we walked / went

So:

• Мы шли сквозь лес, когда начался дождь.
  = We were walking through the forest when it started raining.

But by itself:

• Мы шли сквозь лес.
  can also be translated naturally as We walked through the forest, especially if English style prefers a simple past.

The best English translation depends on the surrounding context.

Yes, Russian word order is flexible.

Мы шли сквозь лес is the neutral, straightforward order:

• Мы = subject
• шли = verb
• сквозь лес = prepositional phrase

Other orders are possible, but they change emphasis:

• Сквозь лес мы шли. = Through the forest is where we were going / walking.
• Шли мы сквозь лес. = We were walking through the forest (with a more narrative or contrastive feel).

Russian uses word order more for emphasis and information structure than for basic grammatical roles.

Шли is pronounced approximately shlee.

Two things often make it difficult:

1. шл is a consonant cluster
   English speakers may want to insert a vowel, but in Russian it is pronounced as one cluster: ш-ли, not shi-li.

2. ш is a hard sh sound
   It is not the same as English she exactly, but shlee is a useful approximation.

Also note that и after ш is still written и, even though the pronunciation may sound a bit closer to y than in English machine.

Here лес is singular: forest.

So сквозь лес means through the forest.

If you wanted through the forests, you would use the plural accusative:

• сквозь леса

Compare:

• Мы шли сквозь лес. = We were going through the forest.
• Мы шли сквозь леса. = We were going through the forests.

In your sentence, the speaker is talking about one forest.

Sometimes English may translate it that way, but through the forest is usually the best match.

Сквозь emphasizes movement within and through something, not just crossing over it from one side to another in an abstract way.

So if the image is:

• entering the forest,
• moving among the trees,
• and continuing onward,

then through the forest is the most natural translation.

English across the forest is less common here unless the context really emphasizes crossing from one side to the other.