У жовтні ми гуляємо в лісі.

Because after у / в meaning in, Ukrainian uses the locative (prepositional) case.

• Dictionary form: жовтень = October
• After у / в: у жовтні = in October

So жовтні is the correct case form after the preposition у.

Yes — у жовтні and в жовтні both mean the same thing: in October.

Ukrainian often alternates between у and в for ease of pronunciation and smoother sound. This is very common.

So both are correct:

• У жовтні
• В жовтні

In this sentence, у жовтні simply sounds more natural before ж.

Because after в meaning in, Ukrainian again uses the locative case.

• Dictionary form: ліс = forest
• Locative after в: в лісі = in the forest

So:

• в ліс would usually mean into the forest and would use a different case
• в лісі means in the forest

This is the same idea as:

• в місті = in the city
• в домі = in the house

Гуляємо comes from the verb гуляти.

In this sentence it means something like:

• we walk
• we go for walks
• we stroll
• we spend time walking around

It often has a relaxed sense, not just moving from one place to another. So it is closer to taking a walk / strolling than to simply going somewhere on foot.

Because it is the 1st person plural present tense form: we ...

The verb гуляти conjugates like this in the present:

• я гуляю = I walk / I am walking
• ти гуляєш = you walk
• він/вона гуляє = he/she walks
• ми гуляємо = we walk
• ви гуляєте = you walk
• вони гуляють = they walk

So гуляємо specifically means we walk / we are walking / we go for walks, depending on context.

It can be omitted.

Ukrainian verbs usually show the subject clearly, so гуляємо already tells you the subject is we.

Both are correct:

• У жовтні ми гуляємо в лісі.
• У жовтні гуляємо в лісі.

Including ми can add emphasis or clarity, but it is not always required.

Most naturally, it suggests a habitual or general action:

• In October, we walk in the forest
• In October, we go for walks in the forest

The present tense in Ukrainian often covers both:

• a present action
• a repeated or habitual action

Without extra context, this sentence is usually understood as something that happens regularly in October, not necessarily at this exact moment.

Yes. Ukrainian word order is relatively flexible.

The neutral order here is:

• У жовтні ми гуляємо в лісі.

But other orders are possible, for example:

• Ми гуляємо в лісі у жовтні.
• В лісі ми гуляємо у жовтні.

The basic meaning stays the same, but the focus changes:

• putting У жовтні first emphasizes the time
• putting в лісі first emphasizes the place

So the original sentence sounds natural and neutral, especially if the speaker wants to foreground October.

Yes. Both are correct:

• в лісі
• у лісі

Just like у / в before жовтні, this choice is often about euphony — what sounds smoother.

So these are all fine:

• У жовтні ми гуляємо в лісі.
• У жовтні ми гуляємо у лісі.
• В жовтні ми гуляємо в лісі.

Speakers choose the version that flows best.

It is a normal locative form, but it may look unfamiliar at first.

• ліс = forest
• у / в лісі = in the forest

Many masculine nouns form the locative with -і, especially after prepositions like в, у, на, по.

So while it may seem irregular to an English speaker, it follows a common Ukrainian pattern.