Если глазурь слишком сладкая, я ем только половину кусочка.

Because глазурь is a feminine noun in Russian, so the adjective has to agree with it.

• сладкий = masculine
• сладкая = feminine
• сладкое = neuter

So:

• сладкая глазурь = sweet icing/frosting

Even though глазурь ends in a soft sign ь, it is feminine, and that is something you usually just have to learn with the noun.

Nouns ending in ь can be either masculine or feminine, so the ending alone does not tell you everything.

For example:

• день is masculine
• глазурь is feminine

So with ь nouns, you often need to memorize the gender along with the word. In this sentence, the adjective сладкая confirms that глазурь is feminine.

Слишком means too.

So:

• слишком сладкая = too sweet

It usually goes before the adjective or adverb it modifies:

• слишком сладкая = too sweet
• слишком быстро = too quickly

That is why it appears directly before сладкая.

Because Russian uses a comma to separate the if-clause from the main clause.

• Если глазурь слишком сладкая, я ем только половину кусочка.

This comma is standard in Russian. Even in a short sentence like this, it is normally required.

Here Если means if, but the whole sentence sounds like a general rule or habit, not a one-time future condition.

So the meaning is closer to:

• Whenever the icing is too sweet, I eat only half the piece.

Russian often uses если + present tense, present tense to describe repeated behavior or a general pattern.

Я ем is the present tense of the imperfective verb есть and is used here because the sentence describes a habit or repeated behavior.

• я ем = I eat / I am eating
• я съем = I will eat up / I will finish eating (perfective, one completed action)
• я буду есть = I will be eating / I will eat (future of imperfective)

Since the speaker means something like this is what I do in that situation, я ем is the natural choice.

Because половину is the accusative case, and it is the direct object of ем.

Dictionary form:

• половина = half

In this sentence:

• я ем что? → половину
• I eat what? → half

So the noun has to change form.

Because after words like половина (half), Russian normally uses the genitive case for the thing being divided.

So:

• половина кусочка = half of a piece
• половину кусочка = half of a piece (with половину in accusative because it is the object)

Here:

• кусочек = a small piece
• кусочка = genitive singular of кусочек

This is a very common pattern in Russian:

• чашка чая = a cup of tea
• кусок хлеба = a piece of bread
• половина яблока = half of an apple

Yes. Кусочек is a diminutive form of кусок.

• кусок = a piece, chunk
• кусочек = a little piece, small piece

Diminutives in Russian can show:

• small size
• affection
• a softer, more natural everyday tone

In this sentence, кусочка sounds like a little piece or simply a piece in a natural conversational way.

Yes, literally it does. That may sound a bit unusual in English, but in Russian it can still sound natural depending on context.

It probably means:

• half of the piece being eaten
• half of a slice or bite-sized piece
• the noun for the larger thing is understood from context

Russian often leaves some things implicit if the situation is clear.

The sentence only says кусочка = of a little piece, without naming the larger item directly.

From context, a Russian speaker would probably understand something like:

• a piece of cake
• a pastry
• a dessert

So the exact noun is omitted because it is obvious enough from the situation. Russian often does this when the context makes the meaning clear.

Только means only, and it is placed right before the part it limits.

• я ем только половину кусочка = I eat only half of the piece

Here только emphasizes that the speaker eats just that amount and no more.

If you move только, the emphasis can shift.

Yes, Russian word order is fairly flexible, though the original version is very natural and neutral.

Original:

• Если глазурь слишком сладкая, я ем только половину кусочка.

Possible variations:

• Я ем только половину кусочка, если глазурь слишком сладкая.
• Если глазурь слишком сладкая, только половину кусочка я ем.
  This sounds more marked and emphasizes half the piece.

So the words can move, but the original is the most straightforward way to say it.

Russian does not have articles like English a/an and the.

So:

• глазурь can mean the icing, some icing, or just icing
• кусочка can mean of a piece, of the piece, depending on context

The exact meaning is understood from the situation rather than from articles.

Yes, in natural English that can be a very good translation.

Because the Russian sentence describes a repeated or typical reaction, English may express it as:

• If the icing is too sweet, I only eat half the piece.
• When the icing is too sweet, I only eat half the piece.
• Whenever the icing is too sweet, I only eat half the piece.

All of those can fit, depending on how habitual you want it to sound.

Yes, a bit.

Ем is pronounced approximately like yem.

That is because the letter е at the beginning of a word often sounds like ye.

So:

• ем ≈ yem
• meaning: I eat

This is the 1st person singular form of есть.

No. In Russian, есть can mean two different things in different contexts:

1. есть = to eat
2. есть = there is / there are or an old/formal is

In this sentence, ем clearly comes from есть meaning to eat.

So:

• я ем = I eat

Not:

• I am

That is a common point of confusion for learners.