I efteråret læser jeg mere derhjemme, fordi regnen ofte holder mig indenfor.

Danish main clauses usually follow the V2 rule: the finite verb comes in the second position.

So when the sentence starts with the time expression I efteråret, the verb læser must come next, and the subject jeg comes after it.

• Jeg læser mere derhjemme.
• I efteråret læser jeg mere derhjemme.

That word order is completely normal in Danish.

Danish normally uses a preposition with seasons in time expressions. So i efteråret means in the autumn / during autumn.

A bare noun like efterår would not usually be used by itself in this kind of sentence.

With seasons, Danish often uses the definite form in common time expressions:

• i foråret
• om sommeren
• i efteråret
• om vinteren

So the -et in efteråret is part of the normal idiomatic pattern. It does not necessarily add a strong extra sense of definiteness in the way an English learner might expect.

They are very close, but there can be a small nuance.

• om efteråret often means in autumn / every autumn as a general recurring habit
• i efteråret often means during the autumn period, and it can also be understood as a more specific autumn depending on context

In everyday use, they overlap a lot. In a sentence about a general habit, many Danes might also say Om efteråret læser jeg mere derhjemme.

Mere means more, but Danish does not have to state the comparison explicitly.

So læser jeg mere can mean:

• I read more than usual
• I read more than in other seasons
• I read more than I otherwise do

The exact comparison is understood from context.

Both can mean at home.

Derhjemme often gives a slightly stronger sense of at home / back home / at my place, while hjemme is a bit more neutral and simple.

In this sentence, both would work, but derhjemme sounds very natural.

Because fordi introduces a subordinate clause.

In subordinate clauses, Danish does not use the same word order as in main clauses. The usual pattern is:

fordi + subject + adverb + verb

So:

fordi regnen ofte holder mig indenfor

is standard Danish.

This is different from main-clause word order, where the verb would normally come earlier.

In a subordinate clause, words like ofte commonly come before the finite verb.

So after fordi, the order is:

• regnen = subject
• ofte = adverb
• holder = finite verb

That is why you get fordi regnen ofte holder mig indenfor.

Regn is the basic noun meaning rain, but regnen is often more natural when the rain is the thing acting on someone in the sentence.

Danish often uses the definite form with familiar natural phenomena in this kind of context:

• regnen
• vinden
• sneen

So regnen ofte holder mig indenfor sounds natural and idiomatic.

Literally, it means keeps me inside.

The verb holde does not only mean hold with the hands. It can also mean keep in many expressions:

• holde nogen vågen = keep someone awake
• holde nogen hjemme = keep someone at home
• holde nogen indenfor = keep someone indoors

So this is a very normal Danish use of holde.

Because mig is the object form of jeg.

• jeg = I
• mig = me

In regnen ofte holder mig indenfor, the rain is doing the action, and mig is the person affected by it. So the object form is required.

Yes. Here indenfor is an adverb meaning inside / indoors, so it is written as one word.

Compare:

• Jeg bliver indenfor. = I stay indoors.
• inden for døren = inside the door area

In the second example, inden for is two words because it is functioning differently. In your sentence, indenfor as one word is correct.