Jeg bruger linealen, når jeg vil tegne en lige streg.

Because linealen is the definite form: the ruler.

In Danish, the definite article is usually attached to the end of the noun:

• en lineal = a ruler
• linealen = the ruler

So:

• Jeg bruger linealen = I use the ruler

By contrast:

• en lige streg = a straight line

That one is indefinite, so it uses en in front.

In Danish, the is often not a separate word the way it is in English. Instead, it is usually added as an ending to the noun.

For common-gender nouns:

• en bog = a book
• bogen = the book

For neuter nouns:

• et hus = a house
• huset = the house

So linealen is built from:

• lineal
  • -en

English uses the ruler, but Danish uses linealen.

Because streg is a common-gender noun, so its indefinite article is en.

The phrase breaks down like this:

• en = a
• lige = straight
• streg = line / stroke

So en lige streg means a straight line.

A useful thing to notice is that the adjective comes before the noun, just as in English:

• en lang streg = a long line
• en lige streg = a straight line

Yes — lige can mean different things depending on context.

In this sentence, lige means straight:

• en lige streg = a straight line

But in other contexts, lige can mean things like:

• just
• exactly
• right / even

For example:

• Jeg kommer lige nu. = I’m coming right now.
• Det er lige præcis det. = That is exactly it.

So learners often get confused by lige, and that is completely normal. Here, because it describes streg, it clearly means straight.

Because vil adds the idea of wanting to or intending to.

• jeg tegner = I draw / I am drawing
• jeg vil tegne = I want to draw

So:

• når jeg vil tegne en lige streg means when I want to draw a straight line

If you said når jeg tegner en lige streg, that would mean:

• when I draw a straight line

That changes the meaning slightly. The original sentence focuses on the speaker’s intention or need.

Because after a modal verb like vil, Danish normally uses the bare infinitive, just like English does after will, can, must, etc.

So:

• jeg vil tegne = I want to draw
• jeg kan tegne = I can draw
• jeg skal tegne = I have to draw

Not:

• jeg vil at tegne

That would be incorrect.

So tegne is the infinitive, and it follows the modal verb vil directly.

Because after a conjunction like når (when), Danish uses subordinate clause word order.

In a main clause, Danish usually follows the V2 rule: the finite verb comes in second position.

Example:

• Jeg bruger linealen.

Here bruger is the finite verb, and it is in second position.

But after når, you get a subordinate clause:

• når jeg vil tegne en lige streg

In subordinate clauses, the subject usually comes before the finite verb in a more English-like order:

• når jeg vil ...
• not når vil jeg ...

So this is normal subordinate-clause word order.

Because når jeg vil tegne en lige streg is a subordinate clause.

Danish punctuation normally separates a main clause from a subordinate clause with a comma:

• Jeg bruger linealen, når jeg vil tegne en lige streg.

Main clause:

• Jeg bruger linealen

Subordinate clause:

• når jeg vil tegne en lige streg

English punctuation is sometimes less strict in similar cases, but in Danish the comma here is standard.

No, Danish normally needs the subject to be stated in each clause.

So you say:

• Jeg bruger linealen, når jeg vil tegne en lige streg.

Even though both clauses have the same subject (I), Danish still repeats jeg in the subordinate clause.

That is similar to English:

• I use the ruler when I want to draw a straight line.

You would not normally say:

• I use the ruler when want to draw...

So the repeated jeg is necessary.

Here når means when in the sense of whenever / at the times that.

So the sentence describes a habitual situation:

• I use the ruler when(ever) I want to draw a straight line.

Danish often uses:

• når for something that happens regularly or is expected
• hvis for if

Compare:

• Jeg bruger linealen, når jeg vil tegne en lige streg. = I use the ruler when I want to draw a straight line.

• Jeg bruger linealen, hvis jeg vil tegne en lige streg. = I use the ruler if I want to draw a straight line.

Sometimes both are possible, but når sounds natural for a general repeated situation.

Because Danish, like English, often uses the present tense for general habits or regular actions.

So:

• Jeg bruger linealen ... means I use the ruler ...

It does not have to mean only what is happening right now. It can mean a general fact about what the speaker usually does.

This is very common in Danish:

• Jeg cykler til arbejde. = I bike to work.
• Hun drikker kaffe om morgenen. = She drinks coffee in the morning.

So the present tense here expresses a habit.

Yes, you could, but the meaning changes slightly.

• Jeg bruger linealen = I use the ruler
• Jeg bruger en lineal = I use a ruler

The definite form linealen suggests a specific ruler, or perhaps the ruler that is understood from the situation.

The indefinite form en lineal is more general and means any ruler / a ruler.

Both are grammatically fine, but they do not mean exactly the same thing.

Tegne is the infinitive form of the verb, meaning to draw.

Some common forms are:

• at tegne = to draw
• tegner = draws / draw
• tegnede = drew
• har tegnet = have/has drawn

In the sentence, it appears without at because it follows the modal verb vil:

• jeg vil tegne

Not exactly.

Both can sometimes be translated as line, but they are used a bit differently.

• streg often means a physical mark, stroke, or drawn line
• linje often means a line in a broader sense, such as a row, route, or abstract line

In this sentence, streg is the natural word because it is a line you draw on paper.

So:

• en lige streg = a straight drawn line

That sounds more natural than en lige linje in this context.

A rough guide is:

• linealen ≈ lee-NAY-len

A few things to notice:

• the stress is typically on the -al- / -eal- part
• the final -en is usually fairly light
• Danish pronunciation is often softer and more reduced than spelling suggests

If you want to build it from the base noun:

• lineal = ruler
• linealen = the ruler

A learner-friendly approach is to listen for the rhythm rather than trying to pronounce every written vowel very clearly.