Wǒ de fángjiān bú dà, dànshì yǒu liǎng gè chuānghu, hěn shūfu.

的 marks possession or association. So 我的房间 means my room.

A simple pattern is:

• 我 = I / me
• 我的 = my
• 我的房间 = my room

In Mandarin, this is very common:

• 我的书 = my book
• 他的老师 = his teacher
• 我们的家 = our home

In Mandarin, adjectives can act like verbs, so you usually do not need 是 before them.

So you say:

• 房间不大 = The room is not big
• 房间很舒服 = The room is comfortable

Not:

• 房间是大
• 房间是舒服

是 is mainly used when one noun equals another noun, such as:

• 我是学生 = I am a student
• 这是我的房间 = This is my room

In Mandarin, a very natural way to say not big is simply 不大.

• 大 = big
• 不大 = not big / not very big

You can sometimes hear 不太大 for not too big, but 不很大 is much less natural in everyday speech.

So:

• 我的房间不大 = My room is not big

This is a normal, idiomatic Mandarin pattern.

This is a tone change rule. 不 is normally fourth tone: bù. But when it comes before another fourth-tone syllable, it changes to second tone: bú.

Here:

• 大 (dà) is fourth tone
• so 不大 is pronounced bú dà

Examples:

• 不是 → bú shì
• 不对 → bú duì
• 不大 → bú dà

The character is still written 不; only the pronunciation changes.

When two comes before a measure word or classifier, Mandarin usually uses 两 rather than 二.

So you say:

• 两个窗户 = two windows
• 两个人 = two people
• 两本书 = two books

Using 二个窗户 would sound unnatural in standard Mandarin.

二 is more common in counting, numbers, math, dates, phone numbers, and set expressions, for example:

• 一，二，三
• 二月 = February
• 二十 = twenty

个 is a measure word or classifier. In Mandarin, when a number modifies a noun, you usually need a classifier between them.

Pattern:

• number + classifier + noun

So:

• 两 + 个 + 窗户
• two + classifier + windows

个 is the most general classifier and is very common.

More examples:

• 一个人 = one person
• 三个苹果 = three apples
• 四个房间 = four rooms

Mandarin nouns usually do not change form for singular vs. plural.

So:

• 窗户 can mean window or windows
• the number is shown by context or by words like 一个, 两个, etc.

Here, 两个窗户 clearly means two windows.

This is different from English, where window and windows have different forms.

Here 有 means to have or to contain.

So:

• 有两个窗户 = has two windows / there are two windows

In this sentence, it describes what the room has:

• 我的房间不大，但是有两个窗户
• My room isn’t big, but it has two windows

Mandarin often uses 有 this way to talk about what something possesses.

In Mandarin, when an adjective is used as a predicate in a simple positive statement, it often needs a word like 很 before it.

So:

• 房间很舒服 sounds natural
• 房间舒服 can sound incomplete in many contexts, or like a contrast

In many cases, 很 does not always mean a strong very. Sometimes it simply helps make the sentence sound natural.

So 很舒服 can mean:

• comfortable
• quite comfortable
• very comfortable

The exact strength depends on context.

In this sentence, 舒服 describes the overall feeling of the room: it is a comfortable room to be in.

Mandarin often allows this kind of expression naturally. Even though 舒服 is about comfort as a feeling, it can describe places, clothes, chairs, weather, and so on:

• 这个椅子很舒服 = This chair is comfortable
• 这个房间很舒服 = This room is comfortable
• 今天天气很舒服 = The weather is comfortable / pleasant today

So here it means the room feels comfortable, probably because it has two windows.

Mandarin often omits a repeated subject when it is obvious from context.

So after saying:

• 我的房间不大，但是有两个窗户

the phrase:

• 很舒服

naturally continues to describe the same room.

A fuller version could be:

• 我的房间不大，但是有两个窗户，所以很舒服。
• 我的房间不大，但是有两个窗户，它很舒服。

But these are less concise or less natural in this context. The original sentence is smooth and natural.

但是 means but / however. It introduces a contrast.

Here the contrast is:

• 我的房间不大 = My room is not big
• 但是有两个窗户 = but it has two windows

So the speaker is saying that although the room is small, it has a positive feature.

Other examples:

• 他很忙，但是很开心。 = He is busy, but happy.
• 这个菜很便宜，但是不好吃。 = This dish is cheap, but not tasty.

房间 means room, while 房子 usually means house or building/home.

So:

• 我的房间 = my room
• 我的房子 = my house

If the meaning shown to the learner is my room, then 房间 is exactly the right word.

Yes, a couple of them often are:

• 的 is usually neutral tone: de
• the second syllable of 窗户 is often neutral: chuānghu
• the second syllable of 舒服 is often neutral: shūfu

So the rhythm is something like:

• wǒ de fángjiān bú dà, dànshì yǒu liǎng gè chuānghu, hěn shūfu

This is useful because English speakers often try to stress every syllable equally, but Mandarin commonly uses neutral tones in very frequent syllables.

Yes, but the nuance changes a little.

• 不大 = not big
• 小 = small

So:

• 我的房间不大 sounds a bit softer and more neutral
• 我的房间很小 sounds more direct: My room is small

In many situations, 不大 is a more natural and less blunt way to describe size.

A useful breakdown is:

• 我的房间 = my room
• 不大 = is not big
• 但是 = but
• 有两个窗户 = has two windows
• 很舒服 = is comfortable

So the structure is roughly:

• topic/subject + description, but + another description, final comment

You can think of it as:

• My room isn’t big, but it has two windows, so it’s comfortable.

Even though Mandarin does not explicitly say so, that result is understood from context.