Doe het deksel op de pan, anders wordt de soep koud.

Doe is the imperative form of doen here, so it is giving a command or instruction: Put the lid on the pan.

In this sentence, doen does not mean the basic English verb to do. In everyday Dutch, iets op iets doen can mean to put something on something.

So:

• doen = to do / to put
• Doe het deksel op de pan = Put the lid on the pan

Dutch nouns have two definite articles:

• de
• het

You simply have to learn which noun takes which article.

In this sentence:

• het deksel = the lid
• de pan = the pan
• de soep = the soup

A useful point: most singular nouns take de, while het nouns are less common and often just need to be memorized.

Here op means that the lid is being placed on / onto the pan.

Dutch often uses op both for:

• a position: on
• movement toward that position: onto

The verb and context tell you which one is meant.

So in:

Doe het deksel op de pan

the idea is clearly movement: put the lid onto the pan.

Dutch uses op because a lid is thought of as something placed on top of the pan.

• op de pan = on the pan
• aan de pan would suggest attachment to the pan, which is not natural here
• over de pan means over the pan, not necessarily touching it

So op de pan is the normal choice for a lid.

Yes, you can. Leg het deksel op de pan is also natural and means almost the same thing.

The difference is mostly one of verb choice:

• doen is very common in everyday Dutch for putting things somewhere
• leggen literally means to lay/place

So both work, but doen is especially common in spoken Dutch.

Anders here means otherwise.

So:

• Doe het deksel op de pan, anders wordt de soep koud.
• Put the lid on the pan, otherwise the soup will get cold.

In other contexts, anders can also mean different(ly), but here the meaning is clearly otherwise.

This is because Dutch is a verb-second language in main clauses.

After anders, the finite verb comes next:

• Anders wordt de soep koud.

Structure:

• anders = first element
• wordt = finite verb in second position
• de soep = subject
• koud = adjective

So although de soep wordt koud is also a normal clause by itself, when anders is placed first, inversion happens:

• De soep wordt koud.
• Anders wordt de soep koud.

Because the sentence means the soup will become/get cold, not that it is cold already.

• is koud = is cold
• wordt koud = gets/becomes cold

So:

• De soep is koud = The soup is cold
• De soep wordt koud = The soup is getting cold / will get cold

That is why wordt is the natural choice here.

Because koud is being used as a predicate adjective, after the verb worden.

Predicate adjectives in Dutch do not take the -e ending:

• De soep wordt koud.
• De pan is heet.

You use koude when the adjective comes before a noun:

• de koude soep = the cold soup

So compare:

• de koude soep = adjective before noun
• de soep wordt koud = adjective after verb

Wordt is the third person singular present tense of worden.

Here the subject is de soep, which is singular, so Dutch uses wordt:

• ik word
• jij wordt / word
• hij/zij/het wordt
• de soep wordt

So wordt matches the singular subject de soep.

It is neutral everyday Dutch.

The imperative Doe ... can be used in normal spoken language when telling someone to do something. Whether it sounds friendly or direct depends mostly on context and tone of voice.

For example:

• in a kitchen, this sounds like a normal instruction
• in a different situation, the same form could sound more abrupt

If you wanted to sound softer, Dutch often adds words like:

• even = just / for a moment
• alsjeblieft = please

For example:

• Doe even het deksel op de pan.

Yes. The comma separates two main clauses:

• Doe het deksel op de pan
• anders wordt de soep koud

This is very natural in Dutch, just like in English:

• Put the lid on the pan, otherwise the soup will get cold.

The comma helps show the pause and the cause-and-result relationship between the two parts.