Не волнуйся, это всего лишь учебная тревога.

Не волнуйся is the informal singular imperative of волноваться — don’t worry.

• волноваться = to worry / to be anxious
• волнуйся = worry! / be worried!
• не волнуйся = don’t worry

By contrast, ты не волнуешься means you are not worrying or you aren’t worried, which is a statement, not a command.

So:

• Не волнуйся. = Don’t worry.
• Ты не волнуешься. = You’re not worried.

The sentence is telling someone not to worry, so the imperative is needed.

Because the verb is волноваться, a reflexive verb ending in -ся.

Russian often forms imperatives from the verb stem, and with reflexive verbs the -ся / -сь remains:

• волноваться → волнуйся (informal singular)
• волноваться → волнуйтесь (plural or polite)

The -ся here is just part of the verb. You should learn волноваться as a whole word, not as волновать + ся for beginner purposes.

A useful comparison:

• успокойся = calm down
• не волнуйся = don’t worry

Both are common reflexive imperatives.

Yes. Не волнуйся is for:

• one person
• someone you address with ты
• informal situations

The polite/plural version is:

• Не волнуйтесь.

So:

• Не волнуйся, это всего лишь учебная тревога. = talking to one friend, child, family member, etc.
• Не волнуйтесь, это всего лишь учебная тревога. = talking politely to one person or to several people

Всего лишь means just, only, nothing more than.

It adds reassurance or minimization:

• это учебная тревога = it’s a drill / training alarm
• это всего лишь учебная тревога = it’s only a drill

The two words work together as a fixed expression:

• всего literally comes from весь in a form that historically means something like of everything / in all
• лишь means only / merely

But in practice, learners should treat всего лишь as a set phrase meaning:

• only
• just
• merely

Examples:

• Это всего лишь шутка. = It’s only a joke.
• Я всего лишь спросил. = I only asked.

Sometimes, but the meaning and style are a bit different.

• лишь alone can mean only, but it can sound more literary or formal in some contexts.
• всего alone can also sometimes mean only, especially with numbers:
  
  • Ему всего десять лет. = He is only ten years old.

In this sentence, всего лишь is very natural and idiomatic because it strongly gives the sense of don’t worry, it’s nothing serious — just a drill.

So while alternatives may exist, всего лишь is the most natural reassuring phrase here.

Учебная тревога is a standard expression meaning:

• drill
• practice alarm
• training alert

Word by word:

• учебная = training / instructional / for practice
• тревога = alarm / alert

Together, they mean an alarm or emergency alert that is for practice, not real.

This is similar to English expressions like:

• fire drill
• practice alert
• training exercise

Depending on context, Russian may also use other drill-related expressions, but учебная тревога is a common and natural phrase.

Because it agrees with тревога.

In Russian, adjectives must match the noun in:

• gender
• number
• case

Here:

• тревога is feminine singular nominative
• so the adjective must also be feminine singular nominative
• therefore: учебная тревога

Compare:

• учебный план = training/study plan (masculine)
• учебное задание = training/study task (neuter)
• учебная тревога = training alarm (feminine)

Yes — Russian usually does not use a present-tense verb meaning is.

So:

• Это учебная тревога.

literally looks like:

• This/it — training alarm.

But in natural English, that becomes:

• It’s a drill.

Here это points to the situation or sound being discussed: this / it. Russian uses это very often in identification sentences like this.

Examples:

• Это мой брат. = This is my brother.
• Это проблема. = This is a problem.
• Это всего лишь учебная тревога. = It’s only a drill.

So yes, there is no separate word for is in the present tense here.

Because the sentence has two parts:

1. Не волнуйся = Don’t worry
2. это всего лишь учебная тревога = it’s only a drill

The comma separates these parts, much like in English:

• Don’t worry, it’s only a drill.

Russian punctuation often uses commas in places that feel similar to English with introductory commands or linked clauses.

The main stresses are:

• Не волну́йся
• э́то
• всего́ лишь
• уче́бная трево́га

A rough pronunciation guide:

• ne val-nuY-sya
• E-ta
• fsye-VO lish
• u-CHEB-na-ya tre-VO-ga

A couple of useful notes:

• In fast speech, не волнуйся often sounds smooth and connected.
• всего begins with a sound closer to fsy- than a clear English v.
• Stress matters a lot in Russian, so it is worth memorizing these with the stress marks.

It can mean a few related things depending on context:

1. alarm / alert
   • Объявили тревогу. = They announced an alert.
2. anxiety / worry
   • Я чувствую тревогу. = I feel anxiety.
3. alarm signal
   • like a warning siren or emergency state

In учебная тревога, it clearly means alarm/alert, not an emotion.

So even though тревога can sometimes mean anxiety, here the adjective учебная makes the meaning very specific: a practice emergency alarm.

Yes, that is possible, and it also means It’s just a drill.

But the nuance is slightly different:

• всего лишь = only / merely / nothing more than, often strongly reassuring or minimizing
• просто = just / simply, often more conversational and broad in meaning

So:

• Это всего лишь учебная тревога. = It’s only a drill.
• Это просто учебная тревога. = It’s just a drill.

Both are natural, but всего лишь can sound a bit more emphatic in the sense of really, that’s all it is.