Дочка хотела раскрасить обложку ярче, но я сказала, что сначала стоит стереть старый рисунок.

Дочка is a more affectionate, everyday form of дочь. Both mean daughter, but:

• дочь = more neutral, dictionary form
• дочка = warmer, more natural in casual speech

So this sentence sounds personal and conversational.

In the past tense, Russian verbs agree with the subject in gender and number.

• дочка хотела = the daughter wanted → feminine singular
• я сказала = I said → the speaker is female

If the speaker were male, it would be я сказал.

Because обложку is the direct object of раскрасить.

The noun обложка is feminine, and feminine nouns in -а usually change to -у in the accusative singular:

• nominative: обложка
• accusative: обложку

So раскрасить обложку means to color the cover.

Раскрасить means to color in / color completely, often with the sense of filling something with colors.

Красить more often means to paint or to dye, and can be broader:

• красить стены = paint walls
• красить волосы = dye hair

Here раскрасить обложку suggests decorating the cover with colors, which fits the context better.

Раскрасить is perfective because it presents the action as a completed whole: finishing the coloring of the cover.

After хотела, Russian can use either aspect depending on the meaning:

• хотела раскрашивать = wanted to be coloring / wanted to spend time coloring
• хотела раскрасить = wanted to color it successfully, to complete it

This sentence focuses on the intended result, so the perfective fits well.

Ярче is the comparative form of яркий / ярко and means brighter, more vividly, or in brighter colors.

In this sentence it works adverbially, describing how she wanted to color the cover:

• раскрасить обложку ярче = color the cover more brightly / make the cover brighter

Russian comparatives often have the same form for adjective-like and adverb-like use, so ярче can mean either brighter or more brightly depending on context.

Но simply means but and links two contrasting ideas:

• the daughter wanted to make the cover brighter
• but the speaker said the old drawing should be erased first

So it works just like but in English.

Что introduces a subordinate clause and means that:

• я сказала, что... = I said that...

In English, that is often optional. In Russian, что is very commonly used and sounds natural here.

Here стоит does not mean stands. It comes from стоить and means something like:

• it is worth
• it would be better
• one should

So:

• сначала стоит стереть старый рисунок = first, it’s worth erasing the old drawing / first, you should erase the old drawing

This is a softer, less direct way to give advice than a command.

Стереть is the perfective form, meaning to erase completely.

The idea is that before doing the new coloring, the old drawing should be removed as a finished step:

• стереть = erase it off, complete the action
• стирать = be erasing, erase repeatedly, or talk about the process in general

Because the sentence is about completing that action first, стереть is the natural choice.

It is in the accusative because it is the object of стереть, but рисунок is masculine and inanimate.

For masculine inanimate nouns, the accusative singular is the same as the nominative:

• nominative: старый рисунок
• accusative: старый рисунок

So the form does not visibly change, even though the case has changed.

That is normal in Russian. In сначала стоит стереть старый рисунок, the subject is left unstated because it is understood from context.

It means something like:

• first, you should erase the old drawing
• first, it would be best to erase the old drawing

The advice is probably directed at the daughter, but Russian does not have to state that explicitly here.

Сначала means first or at first, and here it marks the order of actions:

1. erase the old drawing
2. then color the cover

Putting сначала before the verb phrase makes that sequence very clear. Russian word order is flexible, but this placement is very natural.