Når vejret er koldt, plejer jeg at drikke te i stuen.

Når means when in the sense of something that happens regularly or whenever a situation occurs.

In this sentence, Når vejret er koldt means when the weather is cold or whenever the weather is cold.

A useful comparison is:

• når = when / whenever
• hvis = if

So Danish uses når here because this is about a usual situation, not a hypothetical one.

Examples:

• Når jeg er træt, går jeg tidligt i seng. = When I am tired, I go to bed early.
• Hvis jeg er træt, går jeg tidligt i seng. = If I am tired, I go to bed early.

Vejr means weather, and vejret means the weather.

Danish often uses the definite form where English also says the weather:

• vejret er koldt = the weather is cold

The -et ending is the definite article for a neuter noun:

• et vejr = a weather
• vejret = the weather

Even though English speakers may think of weather as a general idea, Danish normally says vejret in this kind of sentence.

Because vejr is a neuter noun: et vejr.

When an adjective is used with a neuter noun or in a predicate after er, it often takes -t:

• et koldt værelse = a cold room
• vejret er koldt = the weather is cold

Compare:

• en kold dag = a cold day
• et koldt vejr = cold weather
• vejret er koldt = the weather is cold

So the -t is there because the adjective agrees with the neuter noun vejr.

Here, plejer means usually do or tend to do.

So:

• jeg plejer at drikke te = I usually drink tea / I tend to drink tea

This is a very common Danish way to talk about habits.

Examples:

• Jeg plejer at stå tidligt op. = I usually get up early.
• Hun plejer at cykle på arbejde. = She usually bikes to work.

It does not literally mean to please or to care for here, even though the verb at pleje can have other meanings in other contexts. In this sentence, it is the habitual expression plejer at + infinitive.

This is because Danish follows the verb-second rule in main clauses.

When something other than the subject comes first, the finite verb must come next.

So the structure is:

• Når vejret er koldt, = introductory clause
• plejer = finite verb
• jeg = subject
• at drikke te i stuen = rest of the sentence

So:

• Når vejret er koldt, plejer jeg at drikke te i stuen.

If the sentence began with the subject, it would be:

• Jeg plejer at drikke te i stuen, når vejret er koldt.

Both are correct, but once the time clause comes first, Danish puts the verb before the subject in the main clause.

Because plejer is followed by an infinitive, and in Danish this usually takes at.

So:

• plejer at drikke = usually drink
• plejer at læse = usually read
• plejer at gå = usually go

This is similar to English to in some structures, although English says I usually drink, not I usually to drink. So this is one place where Danish and English structure differ.

Yes, it is commonly used to describe something habitual or typical.

It suggests:

• something you usually do
• something that often happens
• a normal pattern

Examples:

• Jeg plejer at drikke kaffe om morgenen. = I usually drink coffee in the morning.
• De plejer at komme for sent. = They usually arrive late.

For a past habit, Danish often uses plejede at:

• Jeg plejede at spille fodbold. = I used to play football.

So:

• plejer at = usually do
• plejede at = used to do

Because te is being used as an uncountable noun in a general sense.

Just like English says:

• I drink tea not usually
• I drink a tea

Danish works the same way here:

• drikke te = drink tea

You would use an article if you meant a specific serving or type in a specific context:

• en te can sometimes mean a tea in casual speech, especially when ordering, but in ordinary grammar te is usually treated as a mass noun.

So in this sentence, drikke te is the natural choice.

I stuen means in the living room.

The noun is:

• en stue = a living room / sitting room
• stuen = the living room

So:

• i stuen = in the living room

This is the normal preposition:

• i køkkenet = in the kitchen
• i soveværelset = in the bedroom
• i stuen = in the living room

Be aware that stue can have other meanings in some contexts, but in everyday home-related sentences like this, it normally means living room.

Yes, you often can.

• Når vejret er koldt = When the weather is cold
• Når det er koldt = When it is cold

Both are natural, but they are slightly different in focus:

• vejret er koldt explicitly mentions the weather
• det er koldt is more general, like English it is cold

In many everyday situations, Danish speakers would probably say Når det er koldt because it is simpler and very common.

Because Når vejret er koldt is a subordinate clause, and in Danish subordinate clauses are separated from the main clause with a comma.

So:

• Når vejret er koldt, = subordinate clause
• plejer jeg at drikke te i stuen. = main clause

This comma is standard Danish punctuation.

Inside the subordinate clause, the word order is quite straightforward:

• Når = when
• vejret = the weather
• er = is
• koldt = cold

So it follows a pattern like:

• conjunction + subject + verb + complement

That is why it looks similar to English:

• When the weather is cold

The main word-order change happens after the comma, where Danish uses verb-second:

• plejer jeg not
• jeg plejer

Yes. A very natural alternative is:

• Jeg plejer at drikke te i stuen, når vejret er koldt.

This means the same thing.

The difference is mainly emphasis:

• Når vejret er koldt, plejer jeg at drikke te i stuen.
  Emphasizes the condition/time first.
• Jeg plejer at drikke te i stuen, når vejret er koldt.
  Starts with I usually drink tea..., then adds when.

Both are correct and common.