Because пуговица (button) is a feminine noun in Russian.
The demonstrative this has to agree with the noun in gender, number, and case:
So:
Since пуговица is feminine, эта is the correct form.
Because маленькая describes пуговица, and adjectives in Russian must agree with the noun they describe.
Here, пуговица is:
So the adjective also takes the feminine singular nominative form:
So:
In this sentence, маленькая is part of the predicate after an implied is, but it still stays in the nominative and agrees with пуговица.
In Russian, the verb to be is usually omitted in the present tense.
So Russian says:
But in natural English, we translate it as:
This is completely normal in Russian. Compare:
If you want past or future, then forms of быть appear:
The preposition для means for, and it requires the genitive case.
So моё пальто (my coat) changes after для to:
Here:
A useful rule to remember:
Examples:
Because пальто is one of those Russian nouns that are indeclinable, meaning its form stays the same in different cases.
So even though для requires the genitive, пальто still looks like пальто.
What changes instead is the word modifying it:
So the case is still genitive, but only моего visibly changes.
This happens with some borrowed nouns in Russian, especially ones ending in -о, such as:
Examples:
Because моё is the nominative form, but after для you need the genitive.
Compare:
Even though пальто is neuter, the form of my still changes for case.
Here are a few neuter forms of мой:
So моего is correct because the phrase is in the genitive after для.
Слишком means too, in the sense of more than is acceptable / more than needed.
So:
By contrast, очень just means very:
That is an important difference:
So if the meaning is excessively small, use слишком.
Yes. In this sentence, для is the normal word for for in the sense of intended for / suitable for.
So:
Russian often uses для + genitive when talking about purpose, suitability, or relation:
So in your sentence, для expresses that the button is too small in relation to the coat.
Yes, Russian word order is fairly flexible, although some orders sound more natural than others.
The neutral word order here is:
You might also hear:
That version puts extra emphasis on для моего пальто.
In general, the original sentence is the most straightforward and natural if you are simply stating the fact.
Yes. Пуговица is the normal word for a clothing button.
That is exactly the right word for a button on a coat, shirt, jacket, etc.
Be careful, because English button can mean different things, and Russian uses different words depending on context:
So for a coat, пуговица is correct, not кнопка.
Yes, слишком can feel tricky at first.
A rough pronunciation is:
More carefully:
So the whole word is approximately:
The stress is on the first syllable:
This is a very common Russian word, so it is worth practicing as a whole chunk:
Yes, but it sounds different in style.
The adjective мал is a short-form adjective, and short forms are often used to express a state or judgment:
So your original sentence is better for a learner to use in normal conversation, but мала is also correct in the right context.