Вечером я готовлюсь к лабораторной по физике.

Вечером is the instrumental singular of вечер and is very commonly used as an adverbial expression meaning in the evening / during the evening.

This is a standard Russian pattern for parts of the day:

• утром = in the morning
• днём = during the day / in the daytime
• вечером = in the evening
• ночью = at night

So Вечером я готовлюсь... means In the evening, I prepare...

Using в вечер would not sound natural here.

Готовлюсь comes from готовиться, which means to get ready, to prepare oneself, or simply to prepare in the sense of getting ready for something.

The -сь is the reflexive ending (a short form of -ся). In this verb, it is just part of the normal dictionary form:

• готовить = to prepare; also often to cook
• готовиться = to prepare oneself / to get ready / to prepare for something

So here:

• я готовлюсь = I am preparing / I am getting ready

This does not mean literally that the person is physically doing something to themselves in English. It is just how Russian expresses this idea with this verb.

No. Even though готовить can mean to cook, the reflexive verb готовиться usually means to prepare oneself / to get ready / to prepare for something.

Compare:

• Я готовлю ужин. = I am cooking dinner.
• Я готовлю доклад. = I am preparing a report.
• Я готовлюсь к экзамену. = I am preparing for an exam.

So in your sentence, готовлюсь clearly means am preparing for.

After готовиться, Russian normally uses к + dative:

• готовиться к экзамену = to prepare for the exam
• готовиться к уроку = to prepare for the lesson
• готовиться к лабораторной = to prepare for the lab

So лабораторной is in the dative case because it follows к.

Great question. The full expression is often:

• лабораторная работа = laboratory work / lab assignment / lab class

After к, the full dative form would be:

• к лабораторной работе

But in everyday speech, Russians very often shorten this and say simply:

• к лабораторной

This is a common kind of ellipsis: the noun работе is omitted because it is understood from context.

So:

• к лабораторной = for the lab
• full version: к лабораторной работе

По физике means in physics or for physics, depending on context. Here it describes what subject the lab is in.

The preposition по often means in the subject of / on / concerning, and in this use it takes the dative case:

• по математике = in math
• по истории = in history
• по физике = in physics

So физике is the dative singular form of физика.

In the full phrase, you could think of it as:

• лабораторная работа по физике = a physics lab / lab assignment in physics

The fully expanded version would be:

Вечером я готовлюсь к лабораторной работе по физике.

Word-for-word structure:

• Вечером = in the evening
• я = I
• готовлюсь = am preparing / am getting ready
• к лабораторной работе = for the lab assignment / lab work
• по физике = in physics

In natural English, this might be:

• In the evening I prepare for my physics lab.
• In the evening I study for the physics lab.
• In the evening I get ready for the physics lab.

Russian has no articles. There is no direct equivalent of a or the.

So к лабораторной по физике could be understood in English as:

• for the physics lab
• for a physics lab

Which one sounds better depends on context. Russian leaves that unstated unless something else makes it clear.

Yes. Russian word order is fairly flexible.

All of these are possible:

• Вечером я готовлюсь к лабораторной по физике.
• Я вечером готовлюсь к лабораторной по физике.
• Я готовлюсь вечером к лабораторной по физике.

The version with Вечером first is very natural if you want to set the time frame right away: In the evening...

Russian word order often changes for emphasis, topic, and flow rather than basic grammar.

Formally, готовлюсь is present tense of the imperfective verb готовиться.

It usually means one of these, depending on context:

• I am preparing
• I prepare
• sometimes I will be preparing

In your sentence, with вечером, it most naturally means something like:

• In the evening I prepare...
• In the evening I am getting ready...

If someone wanted to stress a one-time future completion less vaguely, they might use context or a different aspect, but готовиться is normally the verb used for the process of preparation.

Because готовиться works differently from English.

In Russian:

• готовить что-то = to prepare something
• готовиться к чему-то = to prepare for something

So Russian uses two different verb patterns:

1. Non-reflexive for preparing an object

   • Я готовлю доклад. = I am preparing a report.

2. Reflexive for getting ready for an event/task

   • Я готовлюсь к докладу. = I am preparing for the report/presentation.

That is exactly why your sentence has готовлюсь к лабораторной, not a direct object.

Yes. In real usage, лабораторная can refer to several closely related things, depending on context:

• a lab class
• a lab session
• a lab assignment
• lab work

That is because it is a shortened form of лабораторная работа, and English does not map perfectly onto that phrase in every situation.

So the best translation depends on the situation, not just the grammar.

Yes, it sounds natural.

Especially natural features are:

• вечером for in the evening
• готовлюсь к for prepare for
• the shortened colloquial к лабораторной instead of the full к лабораторной работе
• по физике to show the subject

So this is a very normal everyday Russian sentence.