Возьми широкую кисть, если хочешь закрасить фон быстрее.

Both can mean take, but they are different aspects.

• Возьми is perfective. It sounds like take it now / take one specific brush.
• Бери is imperfective. It often sounds more like go ahead and take / you can take / take habitually.

In this sentence, the speaker is giving a concrete instruction, so Возьми is the natural choice.

Because кисть is the direct object of Возьми, so it goes into the accusative case.

• Dictionary form: широкая кисть = a wide brush
• After take: возьми широкую кисть = take a wide brush

Since кисть is feminine, the adjective must agree with it:

• nominative feminine: широкая
• accusative feminine: широкую

In Russian, every noun has grammatical gender. Кисть is a feminine noun.

You can see that from:

• its dictionary form ending in -ь
• the agreement with the adjective: широкая кисть

Not all nouns ending in -ь are feminine, but many are. Gender has to be learned with each noun.

No. Кисть has several meanings in Russian, depending on context. Common ones include:

• paintbrush / brush
• hand in the sense of the wrist/hand area
• a cluster, for example a bunch of grapes

Here, because of закрасить фон and широкую, it clearly means a paintbrush.

Russian often leaves out subject pronouns when they are clear from the verb form.

• хочешь already means you want
• so если хочешь = if you want

You could say если ты хочешь, but ты is not necessary unless you want extra emphasis or contrast.

Закрасить is a perfective verb. Here it means something like:

• to cover with paint
• to paint over
• to fill in with color completely

The prefix за- often gives the idea of covering or completing the action.

So закрасить фон is not just paint the background in a general sense, but more specifically cover/fill the background with paint.

After хотеть in Russian, you normally use an infinitive:

• хочу читать = I want to read
• хочешь закрасить = you want to paint over / fill in

The perfective infinitive закрасить is used because the idea is to achieve a result: finishing the background faster.

If you used закрашивать instead, it would sound more like an ongoing process rather than the completed result.

Because фон is also the direct object of закрасить, and for an inanimate masculine noun, the accusative looks the same as the nominative.

• nominative: фон
• accusative: фон

So закрасить фон is grammatically normal.

Быстрее is the comparative form of быстро.

• быстро = quickly
• быстрее = more quickly / faster

So закрасить фон быстрее means to paint the background faster.

Russian often uses this simple comparative form without an extra word like more.

No, Russian word order is fairly flexible, though some orders sound more natural than others.

The given sentence:

• Возьми широкую кисть, если хочешь закрасить фон быстрее.

is natural and neutral.

You could also rearrange parts for emphasis, for example:

• Если хочешь закрасить фон быстрее, возьми широкую кисть.

That version puts the condition first: If you want to paint the background faster, take a wide brush.

Yes, если often means if, and in some contexts it can correspond to whether. In this sentence it clearly means if:

• если хочешь = if you want

So the structure is:

• instruction: Возьми широкую кисть
• condition: если хочешь закрасить фон быстрее

Yes. Even though Возьми is literally an imperative, in context it can function as practical advice:

• Take a wide brush if you want to paint the background faster
• or more naturally in English: Use a wide brush if you want to cover the background faster

Russian imperatives are often used for instructions, recommendations, and tips, not only strict commands.