Суп ещё не готов: его нужно доварить ещё пять минут.

Not quite.

• In Суп ещё не готов, ещё means yet / still.
  So this part means The soup isn’t ready yet.

• In ещё пять минут, ещё means another / five more.
  So this part means for another five minutes or five more minutes.

This is very common in Russian: the same word ещё can mean either still/yet or more/another, depending on context.

Готов is the short form of the adjective готовый.

In Russian, short-form adjectives are often used:

• as the main predicate
• especially for temporary states or conditions

So:

• Суп готов. = The soup is ready.
• Суп не готов. = The soup is not ready.

Using готовый here would sound wrong in normal speech. Готовый is the full form and is used more like an attributive adjective:

• готовый суп = ready soup

So in this sentence, you need готов, not готовый.

In the present tense, Russian usually omits the verb to be.

So:

• Суп готов literally looks like Soup ready
• but it means The soup is ready

This is normal Russian grammar.

Compare:

• Он дома. = He is at home.
• Она занята. = She is busy.

In past and future tense, forms of быть do appear:

• Суп был готов. = The soup was ready.
• Суп будет готов. = The soup will be ready.

Его is the pronoun meaning it / him, depending on context. Here it refers to суп, so it means it.

Why this form? Because его is the direct object form of the pronoun:

• суп = the soup
• доварить суп = to finish cooking the soup
• доварить его = to finish cooking it

So:

• его нужно доварить = it needs to be cooked a bit more / it needs finishing

Even though суп is inanimate, the pronoun is still его.

Нужно is an impersonal word meaning it is necessary, one needs to, or must in a general sense.

So:

• его нужно доварить literally = it is necessary to finish cooking it
• natural English = it needs to be cooked a bit longer / you need to cook it a bit more

This construction is extremely common:

• Нужно подождать. = It’s necessary to wait.
• Нужно идти. = We need to go.
• Мне нужно работать. = I need to work.

In your sentence, there is no specific subject like я or ты. It is just a general statement of necessity.

Доварить means to finish cooking, to cook a bit longer until done.

It comes from:

• варить = to cook, boil
• prefix до- = up to the end / to completion / finish doing something

So доварить suggests:

• the soup has already been cooking
• but it is not quite done
• it needs a little more cooking to reach completion

Compare:

• варить = to cook / be cooking
• сварить = to cook completely / prepare by boiling
• доварить = to finish cooking something that is already partly cooked

That makes доварить especially natural here, because the first clause says the soup is not ready yet.

Because the sentence is about reaching a result: the soup should become fully ready after those five minutes.

Perfective verbs in Russian often focus on:

• completion
• a single finished action
• achieving a result

Here, доварить means cook it until it is done.

If you used the imperfective доваривать, it would sound more like:

• a repeated process
• an ongoing action
• or a more process-oriented viewpoint

You could also hear варить ещё пять минут, which is possible and natural, but доварить adds the idea of finishing it off.

Because after 5 and higher numerals, Russian uses the noun in the genitive plural.

So:

• одна минута
• две / три / четыре минуты
• пять минут
• десять минут

That is why the sentence has:

• ещё пять минут = another five minutes

This is one of the standard number patterns in Russian and is worth memorizing.

Because Russian often uses a bare time expression to show duration.

So:

• варить суп пять минут = to cook the soup for five minutes
• подождать минуту = to wait a minute
• работать весь день = to work all day

In this sentence:

• доварить ещё пять минут = cook it for another five minutes

Using на пять минут would usually give a different meaning and would not be the normal way to express simple duration here.

The colon shows that the second part explains or follows from the first part.

So the logic is:

• Суп ещё не готов
  The soup isn’t ready yet
• его нужно доварить ещё пять минут
  it needs another five minutes of cooking

The second clause gives the practical conclusion from the first one.

In English, you might use:

• a colon
• a dash
• or just a full stop

Russian punctuation here is quite natural and slightly formal/written in tone.

Yes, you could, especially in less formal writing or speech.

But the colon is useful because it makes the relationship clearer:

• first statement: the soup is not ready
• second statement: therefore it needs more cooking

So:

• Суп ещё не готов: его нужно доварить ещё пять минут.
  sounds neat and explanatory.

A comma version may be seen, but the colon is better punctuation for this exact structure.

Both are possible, but they are slightly different.

• его нужно доварить explicitly says it needs to be finished
• нужно доварить ещё пять минут without его sounds more incomplete unless the object is very obvious from context

Since the first clause mentions суп, using его helps keep the sentence clear and natural.

Russian often repeats an object with a pronoun like this:

• Книгу я прочитал. Её было интересно читать.
• Суп не готов. Его нужно доварить.

So the pronoun makes the link smooth and explicit.

Yes, more or less. A very literal breakdown would be:

• его = it
• нужно = it is necessary / need to
• доварить = finish cooking
• ещё пять минут = another five minutes

So the literal structure is close to:

It is necessary to finish cooking it another five minutes.

But natural English would be:

• It needs to cook for another five minutes
• You need to cook it for another five minutes
• The soup needs another five minutes

All of those capture the Russian meaning well.