Моя подруга любит тёплый круассан с маслом и джемом.

Because подруга is a feminine noun. In Russian, possessive words like мой / моя / моё / мои must agree with the noun in gender and number.

• мой = masculine singular
• моя = feminine singular
• моё = neuter singular
• мои = plural

So:

• мой друг = my male friend
• моя подруга = my female friend

For the same reason: adjectives must agree with the noun they describe.

Круассан is a masculine singular noun, so the adjective must also be masculine singular:

• тёплый круассан = a warm croissant

Compare:

• тёплая булочка = a warm bun/pastry
• тёплое молоко = warm milk
• тёплые круассаны = warm croissants

It is accusative, but for inanimate masculine singular nouns, the accusative often looks exactly like the nominative.

So:

• nominative: круассан
• accusative: круассан

That is why there is no visible change.

Compare with an animate masculine noun:

• Я вижу брата = I see my brother

Here брат changes to брата in the accusative because it is animate.

But with inanimate nouns:

• Я люблю круассан = I love/like croissant

No visible change.

Because the preposition с meaning with normally requires the instrumental case.

Dictionary forms:

• масло
• джем

Instrumental forms:

• маслом
• джемом

So:

• с маслом = with butter
• с джемом = with jam

That is why the sentence says с маслом и джемом.

Here с means with, and it takes the instrumental case.

So the pattern is:

• с + instrumental

Examples:

• с сыром = with cheese
• с кофе = with coffee
• с другом = with a friend
• с подругой = with a female friend

Be careful: с can also mean from/off in other contexts, and then it may take a different case. But in this sentence, it clearly means with.

Yes. It describes the croissant as being served or eaten with butter and jam.

Russian does not need to repeat с before both nouns here. One с covers both:

• с маслом и джемом = with butter and jam

You could repeat it for emphasis in some contexts, but normally you would not:

• с маслом и с джемом — possible, but less natural here

Yes, it is natural. In Russian, любить can be used directly with foods to mean to like / to love eating them.

So:

• Она любит круассаны = She likes croissants / She loves eating croissants

Russian often does not need a separate verb like eat when the meaning is obvious from context.

If you wanted to be more explicit, you could say something like:

• Моя подруга любит есть тёплые круассаны = My friend likes to eat warm croissants

But the original sentence sounds perfectly normal.

Тёплый usually means warm, not hot.

So тёплый круассан suggests a croissant that is pleasantly warmed, maybe fresh from the oven or reheated a little.

If you said горячий круассан, that would mean hot croissant, which sounds stronger.

So:

• тёплый = warm
• горячий = hot

The letter ё is pronounced roughly like yo.

So тёплый sounds like TYOP-liy.

A very important point: in many Russian texts, ё is often written as е, even though the pronunciation is still ё. So you may also see:

• теплый

But the correct pronunciation is still тёплый.

For learners, writing ё is very helpful because it shows the real pronunciation.

Yes. Russian word order is more flexible than English word order because the grammatical endings carry a lot of information.

The neutral order here is:

• Моя подруга любит тёплый круассан с маслом и джемом.

But other orders are possible depending on emphasis, for example:

• Тёплый круассан с маслом и джемом любит моя подруга.

This puts more focus on what she likes.

Still, for learners, the original version is the safest and most natural neutral order.

It describes only круассан.

The structure is:

• тёплый круассан = warm croissant
• с маслом и джемом = with butter and jam

So the meaning is:

• a warm croissant
• that comes with butter and jam

It does not mean that the butter and jam are warm.

Because подруга specifically means a female friend, while друг means a male friend.

So:

• друг = male friend
• подруга = female friend

English uses friend for both, but Russian usually makes the gender clear in the noun itself.

It is a borrowed word, originally from French (croissant), but it is fully used as a normal Russian noun.

In Russian it behaves like a regular masculine noun:

• круассан
• круассана
• круассану
• круассан
• круассаном
• о круассане

So even borrowed words usually follow Russian grammar once they are adopted.