Чтобы приготовить омлет, сначала нужно взбить яйца венчиком.

Here чтобы means in order to or simply to when expressing purpose.

So:

• Чтобы приготовить омлет = To make an omelet / In order to make an omelet

A very common pattern in Russian is:

• чтобы + infinitive = in order to do something

This is especially common when the person doing both actions is understood to be the same.

Приготовить is the perfective form, while готовить is imperfective.

• готовить = to cook, to prepare, to be preparing
• приготовить = to prepare/make successfully, to finish making

In this sentence, the idea is about achieving a result: making an omelet. That is why Russian uses the perfective приготовить.

A rough contrast:

• Я люблю готовить омлет. = I like making omelets.
• Я хочу приготовить омлет. = I want to make an omelet.

The same idea appears later with взбить.

Омлет is the direct object of приготовить, so it is in the accusative case.

However, for many masculine inanimate nouns, the accusative singular looks exactly like the nominative singular. So:

• nominative: омлет
• accusative: омлет

So the case does change grammatically, but the form happens to stay the same.

Сначала means at first, first, or to begin with.

So:

• сначала нужно взбить яйца = first you need to beat the eggs

It marks the first step in a process. In cooking instructions, this is very common.

You may also see сперва, which is similar in meaning.

Нужно is an impersonal word meaning it is necessary, one must, or you need to.

So:

• нужно взбить яйца = you need to beat the eggs / it is necessary to beat the eggs

Russian often prefers this impersonal style in instructions, recipes, and general advice because it sounds neutral and natural.

Compare:

• Тебе нужно взбить яйца. = You need to beat the eggs.
• Нужно взбить яйца. = It’s necessary to beat the eggs / One needs to beat the eggs.

In a recipe, the version without a subject is very typical.

Again, this is an aspect choice.

• взбивать = to beat/whisk, to be beating, to beat repeatedly or as a process
• взбить = to beat/whisk successfully, to whip up

In a recipe step, Russian often uses the perfective because the action is viewed as something that should be completed.

So:

• нужно взбить яйца = you need to beat the eggs until that step is done

If you wanted to emphasize the process itself, you might use взбивать in another context, but взбить is the natural choice here.

Яйца is the plural of яйцо (egg), and here it is the direct object of взбить, so it is in the accusative plural.

For inanimate plural nouns, the accusative is usually the same as the nominative. So:

• nominative plural: яйца
• accusative plural: яйца

That is why the form is яйца.

Венчиком means with a whisk.

The base noun is:

• венчик = whisk

Here it appears in the instrumental case:

• венчик → венчиком

The instrumental case is often used to show the tool or means by which something is done.

So:

• взбить яйца венчиком = beat the eggs with a whisk

This is a very common use of the instrumental in Russian.

Russian often leaves out the subject when it is general, obvious, or not important.

In recipes and instructions, English often says:

• First, you need to beat the eggs.

Russian often prefers the more impersonal version:

• Сначала нужно взбить яйца.

This sounds natural and standard in instructional style. It is not missing anything essential; the person meant is understood from context.

No, Russian word order is fairly flexible, but the version here is very natural.

• Чтобы приготовить омлет, сначала нужно взбить яйца венчиком.

This order works well because it goes:

1. purpose
2. first step
3. action
4. object
5. instrument

You could move some parts around for emphasis, for example:

• Сначала, чтобы приготовить омлет, нужно взбить яйца венчиком.
• Яйца сначала нужно взбить венчиком, чтобы приготовить омлет.

But the original sentence is the most straightforward and natural for a recipe-like instruction.

Both verbs are infinitives, but they play different roles.

• Чтобы приготовить омлет = purpose clause: to make an omelet
• нужно взбить яйца = what needs to be done: it is necessary to beat the eggs

So the structure is basically:

• In order to do X, it is necessary to do Y.

This kind of infinitive-heavy structure is very common in Russian instructions and explanations.