Не нужно тратить время.

Because this is an impersonal construction in Russian. Russian often leaves out a subject when the idea is general, like it is not necessary to... or there is no need to...

So:

• Не нужно тратить время = There is no need to spend/waste time
• literally, something like Not necessary to spend time

You do not need a word for it here. English requires it in It is not necessary..., but Russian does not.

Here нужно means necessary, needed, or there is a need.

In this sentence, нужно works as a predicative word, not like a normal adjective modifying a noun. It is part of a common pattern:

• нужно + infinitive = need to / it is necessary to
• не нужно + infinitive = don’t need to / it is not necessary to

Examples:

• Нужно идти. = It is necessary to go / We need to go.
• Не нужно спешить. = No need to hurry.

Both не нужно and не надо are very common, and in many situations they mean almost the same thing:

• Не нужно тратить время
• Не надо тратить время

Both can mean There’s no need to waste time or Don’t waste time, depending on context.

A rough difference:

• не нужно often sounds a bit more neutral or matter-of-fact
• не надо can sound a bit more conversational, stronger, or more like advice/request

But in everyday speech, they overlap a lot.

Because after words like нужно, надо, можно, нельзя, Russian normally uses the infinitive.

So the pattern is:

• нужно делать = need to do
• можно войти = may come in / it is possible to enter
• нельзя курить = must not smoke
• не нужно тратить = don’t need to spend/waste

The infinitive here is the basic dictionary form of the verb.

Because время is the direct object of тратить.

The verb тратить means to spend or to waste, and it takes the accusative case:

• тратить время = to spend/waste time
• тратить деньги = to spend money
• тратить силы = to use up energy

For the noun время, the accusative singular looks the same as the nominative singular:

• nominative: время
• accusative: время

So the form does not visibly change, even though the case function does.

Тратить is imperfective.

That matters because the imperfective is commonly used for:

• general statements
• ongoing actions
• repeated actions
• actions considered as a process

In Не нужно тратить время, the idea is general: there is no need to spend/waste time.

The perfective partner is usually потратить:

• Не нужно тратить время = general statement, no need to spend/waste time
• Не нужно потратить время would be wrong here

If you want perfective after нужно, you would normally use it in a context where completing a single action matters, for example:

• Нужно потратить час на отчёт. = You need to spend an hour on the report.

But in your sentence, the imperfective тратить is the natural choice.

It can suggest either, depending on context.

Literally, тратить means to spend/use up. But with время, it often has a negative flavor, so тратить время very often means waste time.

So:

• Не нужно тратить время often feels like No need to waste time
• but in some contexts it may simply mean No need to spend time on this

If someone wants to make the idea of wasting extra clear, they might say:

• не тратить время зря = not waste time in vain

Yes. That is very common.

Grammatically, не нужно + infinitive means there is no need to... But in real life, it can also function like mild advice or a recommendation:

• Не нужно тратить время. = You don’t need to waste time.
• depending on tone/context: Don’t waste time.

So Russian often leaves the exact force to context and intonation.

Yes. Russian word order is flexible, and changing it usually changes emphasis, not the basic meaning.

Neutral order:

• Не нужно тратить время.

Other possible orders:

• Время тратить не нужно.
• Тратить время не нужно.

These alternatives may emphasize время or тратить время more strongly.

For a learner, the original version is the safest and most neutral one to use.

The stress is:

• Не ну́жно тра́тить вре́мя.

Word by word:

• не
• ну́жно
• тра́тить
• вре́мя

A rough English-style pronunciation guide would be:

• nye NOOZH-na tra-tit VRYE-mya

A few notes:

• нужно is pronounced with stress on ну́-
• время has stress on the first syllable: вре́мя
• the я in время sounds like ya

Yes. This pattern is very productive:

• Не нужно тратить деньги. = No need to spend money.
• Не нужно тратить силы. = No need to waste energy.
• Не нужно тратить нервы. = No need to waste your nerves / No need to get stressed out.

So the model is:

• Не нужно + infinitive + object

In your sentence:

• Не нужно = no need
• тратить = to spend/waste
• время = time