Illalla luen tyttärelleni sadun ennen nukkumaanmenoa.

Because illalla is the adessive form of ilta (evening). In Finnish, parts of the day are often expressed with this case:

• aamulla = in the morning
• päivällä = during the day
• illalla = in the evening
• yöllä = at night

So illalla here means in the evening or, depending on context, tonight.

Finnish word order is fairly flexible. Putting Illalla first makes the time setting the topic of the sentence: As for the evening / In the evening...

That is very natural Finnish. You could also say:

• Luen illalla tyttärelleni sadun ennen nukkumaanmenoa.

That would still be grammatical, but the emphasis would be a little different. Starting with the time expression is common when you want to set the scene first.

Luen is the present tense, first person singular, of lukea (to read): I read / I am reading.

But Finnish often uses the present tense for future meaning when the time is clear from context. Since the sentence already has Illalla, luen can naturally mean:

• I read
• I will read
• I’m going to read

So Finnish does not need a separate future tense here.

Because Finnish packs several meanings into one word.

tyttärelleni breaks down like this:

• tytär = daughter
• tyttärelle = to/for the daughter
• tyttärelleni = to/for my daughter

More specifically:

• tyttäre- = the stem used in many cases
• -lle = allative ending, often meaning to or for
• -ni = possessive suffix meaning my

So tyttärelleni means to my daughter.

Some Finnish nouns have a different stem when case endings are added. tytär is one of them.

For example:

• tytär = daughter
• tyttären = of the daughter
• tyttärelle = to the daughter
• tyttärellä = on/at the daughter

This is just part of how that noun declines. Learners usually need to memorize tytär as a noun with an irregular stem.

Because Finnish can show possession with a suffix attached to the noun.

So:

• tyttärelleni = to my daughter

A separate minun is not necessary. You can say:

• minun tyttärelleni

but that usually adds emphasis, contrast, or clarity. In ordinary speech and writing, the possessive suffix -ni is often enough.

This is about the object case.

Here sadun is a total object: the idea is that the whole story is read, from beginning to end. In this kind of sentence, a singular total object usually appears in the -n form.

So:

• luen sadun = I read a/the whole story
• luen satua = I am reading a story / some story / story material, with no focus on completion

In many grammars, sadun is called the accusative object, although in the singular its form looks the same as the genitive.

It could mean either. Finnish has no articles, so there is no direct equivalent of a or the.

That means sadun could be understood as:

• a story
• the story

The context decides which is meant. The -n ending here marks the object, not definiteness.

nukkumaanmeno is a noun meaning going to sleep or bedtime.

It comes from the idea of mennä nukkumaan = to go to sleep / to go to bed.

So:

• nukkumaanmeno = bedtime / going to sleep
• nukkumaanmenoa = partitive form of that noun

In this sentence, it means before bedtime or before going to sleep.

Because ennen (before) takes the partitive when used as a preposition.

So you get:

• ennen ruokaa = before food / before the meal
• ennen koulua = before school
• ennen nukkumaanmenoa = before bedtime / before going to sleep

That is why the noun appears as nukkumaanmenoa, not in the basic form nukkumaanmeno.

Yes. That would be a very natural alternative.

Compare:

• ennen nukkumaanmenoa = before bedtime / before going to sleep
• ennen kuin menen nukkumaan = before I go to sleep

The first uses a noun phrase, so it feels a bit more compact. The second uses a full clause, which can feel a bit more explicit. Both are correct.

It could be either, depending on context.

Because luen is present tense, the sentence can mean:

• a habit: In the evening I read my daughter a story before bedtime
• a planned event: This evening I’ll read my daughter a story before bedtime

Finnish often leaves that distinction to context rather than marking it directly in the verb form.