Она решила рисовать акварелью, хотя брат сказал, что ему больше нравится мастерить что‑то из картона.

Because the subject is она, so the verb in the past tense must agree with a feminine singular subject.

• он решил = he decided
• она решила = she decided
• оно решило = it decided
• они решили = they decided

In the Russian past tense, gender matters in the singular.

After решила (decided), Russian usually uses an infinitive to say what someone decided to do.

• Она решила рисовать = She decided to paint

This works much like English decided to paint.

Because рисовать is the imperfective verb, and here it suggests the activity in general: she decided to do painting / to paint as an activity.

If you said решила нарисовать, that would more likely mean she decided to paint/create one specific picture.

So:

• решила рисовать = decided to paint, take up painting, do painting
• решила нарисовать = decided to paint/draw something specific

Акварелью is the instrumental case of акварель.

Russian often uses the instrumental to show the means, instrument, or medium by which something is done.

So:

• рисовать акварелью = to paint with watercolor
• compare:
  • писать ручкой = write with a pen
  • резать ножом = cut with a knife

Here акварелью means the artistic medium, not just the physical tool.

Because хотя introduces a subordinate clause meaning although / even though.

Russian normally separates subordinate clauses with commas:

• Она решила рисовать акварелью, хотя брат сказал...

This is very standard punctuation.

Хотя means although, even though, or though.

It introduces a contrast:

• she decided to paint with watercolors
• although her brother said he preferred making things from cardboard

So it shows that his opinion was different, but it did not change her decision.

Что means that when it introduces reported speech or a content clause.

So:

• брат сказал, что... = her brother said that...

This is one of the most common Russian patterns:

• Я знаю, что... = I know that...
• Он думает, что... = He thinks that...
• Она сказала, что... = She said that...

And yes, a comma is normally placed before что in this use.

Because нравиться works differently from English to like.

In Russian, the thing liked is the grammatical subject, and the person who experiences the liking goes in the dative case.

So:

• ему нравится мастерить = making/crafting pleases him = he likes crafting
• literally: to him is pleasing to craft

Examples:

• Мне нравится музыка = I like music
• Ей нравится читать = She likes reading
• Им нравится гулять = They like walking

So ему is dative: to him.

Больше нравится means likes more or prefers.

So:

• ему больше нравится мастерить... = he likes making things more / he prefers making things...

It compares one preference against another, even if the other option is only implied by context.

Мастерить means something like:

• to make by hand
• to craft
• to tinker
• to build little things

It often suggests practical, hands-on creation, especially simple objects, homemade things, or hobby-type projects.

By contrast:

• делать = to do / to make (very general)
• мастерить = to craft/build/tinker with the hands

So мастерить что‑то из картона sounds more natural than делать что‑то из картона if the idea is handicrafts or homemade objects.

Что‑то means something.

The particle -то is added to pronouns to make them indefinite:

• что = what
• что‑то = something
• кто = who
• кто‑то = someone

It is written with a hyphen because that is the standard spelling for these -то forms.

In this sentence, что‑то is the direct object of мастерить:

• мастерить что‑то = to make something

Because из means from / out of, and it requires the genitive case.

• картон → картона

So:

• из картона = out of cardboard / from cardboard

Other examples:

• из дерева = out of wood
• из бумаги = out of paper
• из пластика = out of plastic

Yes, Russian word order is fairly flexible, and the sentence could be rearranged for emphasis.

The given version is neutral and natural:

• Она решила рисовать акварелью, хотя брат сказал, что ему больше нравится мастерить что‑то из картона.

But Russian could move parts around if the speaker wanted to emphasize contrast or topic. For example, акварелью or брат could be placed elsewhere.

Even so, not every rearrangement sounds equally natural. The original is a good standard order for everyday written Russian.

In standard pronunciation, что is usually pronounced closer to што, not exactly as spelled with a clear ч sound.

So:

• что ≈ shto

This is very common and normal in modern Russian pronunciation.

The spelling stays что, but learners should be ready to hear што in real speech.