Det tok meg lang tid å lære å brette laken uten hjelp.

Here det is a dummy subject, just like English it in It took me a long time....

So:

• Det tok meg lang tid ... = It took me a long time ...

The det does not refer to a specific thing. Norwegian often uses det this way in general statements.

Because meg is the object form of the pronoun, while jeg is the subject form.

• jeg = I
• meg = me

In Det tok meg lang tid, the verb tok has meg as its object:

• det = subject
• tok = verb
• meg = object

So Norwegian matches English here: It took me..., not It took I...

Tok is the preterite/simple past of ta.

The main forms are:

• å ta = to take
• tar = takes / is taking
• tok = took
• har tatt = has taken

So det tok meg lang tid literally means it took me a long time.

Because lang tid is a noun phrase meaning a long time, while lenge is an adverb meaning for a long time / long.

Compare:

• Det tok lang tid. = It took a long time.
• Jeg ventet lenge. = I waited a long time.

With ta/tok, Norwegian very often uses tid:

• Det tar tid.
• Det tok lang tid.

So lang tid is the natural choice in this sentence.

In this kind of expression, Norwegian often leaves out the article.

So the normal idiomatic pattern is:

• Det tok lang tid
• Det tok meg lang tid

This works a lot like a fixed time-expression with ta.
Using en lang tid is much less natural here and can sound heavy or unusual.

So for learners, the safest pattern is:

• det tar/tok + lang tid

Because there are two infinitives:

• å lære = to learn
• å brette = to fold

So:

• å lære å brette = to learn to fold

In Norwegian, each infinitive normally keeps its own å.

The structure tells you.

Here you have:

• å lære å brette ... = to learn to fold ...

That pattern means learn to do something.

If lære means teach, it usually has a person as object:

• Jeg lærte ham norsk. = I taught him Norwegian.

Also, lære bort is a very common way to say teach more clearly:

• Hun lærer bort norsk. = She teaches Norwegian.

So in this sentence, lære clearly means learn.

It could. Both are possible:

• å lære å brette
• å lære seg å brette

The version without seg is perfectly natural and common.
Adding seg can put a bit more emphasis on acquiring the skill oneself.

So:

• Det tok meg lang tid å lære å brette laken ...
• Det tok meg lang tid å lære seg å brette laken ...

Actually, the second one would need meg if you use seg with the same subject:

• Det tok meg lang tid å lære meg å brette laken ...

But in everyday Norwegian, many speakers simply say lære å brette here.

No. Norwegian often uses just å + infinitive where English might say either to do or how to do.

So:

• å lære å brette laken = to learn to fold sheets

You could also say something more explicit, such as:

• å lære hvordan man bretter laken

But that is longer and slightly more explanatory. The original sentence is the more natural everyday wording.

Brette means to fold, especially with things like:

• paper
• clothes
• blankets
• sheets

So å brette laken means to fold sheets / bed linen.

It is the normal verb for making something flat or neat by folding it.

In this sentence, laken is most naturally understood as indefinite plural: sheets.

That is because Norwegian often uses a bare plural after a verb when speaking generally:

• å vaske klær = to wash clothes
• å brette laken = to fold sheets

Also, laken is one of those nouns where the indefinite singular and an indefinite plural form can look the same, so context matters.

If the speaker clearly meant one sheet, they would very often say:

• å brette et laken

So here, most learners should understand laken as sheets in a general sense.

Uten hjelp means without help.

There is no article because hjelp is being used in a general, abstract sense, just like in English:

• without help
• uten hjelp

If you want to be more specific, you add more information:

• uten min hjelp = without my help
• uten hjelp fra andre = without help from others

So the bare form uten hjelp is completely normal.