Learn Hardcore Finnish: Uutiskirjeen otsikko on selkeä. - The title of the newsletter is clear.

uutiskirjeen – of the newsletter (genitive singular of uutiskirje “newsletter”)
otsikko – title / headline
on – is (3rd person singular of olla “to be”)
selkeä – clear (adjective)

So the structure is literally: “newsletter’s title is clear.”

Why does uutiskirje become uutiskirjeen here?

Uutiskirjeen is the genitive singular form of uutiskirje (“newsletter”).

The -n ending marks possession, like adding ’s in English.
So uutiskirjeen otsikko = “the newsletter’s title” / “the title of the newsletter.”

In Finnish, when you say “X’s Y”, the owner (X) is put in the genitive case:

ystävä → ystävän talo = friend → the friend’s house
uutiskirje → uutiskirjeen otsikko = newsletter → the newsletter’s title

What case is otsikko in, and why?

Otsikko is in the nominative singular (the basic dictionary form).

In sentences with the verb olla (“to be”), the typical pattern is:

Subject (nominative) + on (is) + predicative (also nominative)

Here:

Subject: (Uutiskirjeen) otsikko = “the title (of the newsletter)”
Verb: on = is
Predicative (complement): selkeä = clear

So otsikko stays in the nominative because it’s the grammatical subject of the sentence.

Why is the adjective selkeä in this form? Shouldn’t it change to agree with otsikko?

Selkeä does agree with otsikko, but in this case the agreement is invisible:

otsikko is nominative singular
The basic form selkeä is also nominative singular

In Finnish, the predicative adjective after olla (“to be”) usually:

matches the subject in number (singular/plural)
and in case, when it’s in a case

Examples:

Otsikko on selkeä. – The title is clear. (singular)
Otsikot ovat selkeitä. – The titles are clear. (plural, partitive plural for a characteristic of multiple items)

So here “clear” in the singular nominative is simply selkeä.

What is the difference between selkeä and selvä? Could I say Uutiskirjeen otsikko on selvä?

You can say Uutiskirjeen otsikko on selvä, and it will be understood, but there is a nuance:

selkeä
- often means clear, easy to see/read/understand, well-structured, unambiguous
- used a lot for layout, wording, instructions, user interfaces, etc.
- sounds slightly more neutral and descriptive here
selvä
- can also mean clear, obvious, definite, and in some contexts “sober” (not drunk), or “all right / OK”
- otsikko on selvä can be understood as “the title is clear/obvious,” but may feel a bit less natural in contexts where you’re evaluating clarity of design or wording

For talking about a well-worded or well-formatted title, selkeä is the most idiomatic choice.

Why is it on and not some other form of the verb “to be”?

On is the 3rd person singular present tense form of olla (“to be”).

Finnish conjugation of olla in the present:

(minä) olen – I am
(sinä) olet – you are (singular)
(hän/se) on – he/she/it is
(me) olemme – we are
(te) olette – you are (plural / formal)
(he/ne) ovat – they are

The subject here is otsikko = “the title”, which is 3rd person singular, so the verb form must be on: otsikko on = “the title is”.

Is uutiskirje a compound word? What are its parts and what do they mean?

Yes, uutiskirje is a compound noun:

uutis- – from uutinen = news item, piece of news; in compounds it appears as uutis-
kirje – letter (as in a written letter)

So literally uutiskirje is a “news letter”, which matches the English newsletter.

In Finnish it’s written as one word, not as two separate words.

Can I change the word order, like Otsikko on selkeä uutiskirjeen or Otsikko uutiskirjeen on selkeä?

These alternatives are not natural in standard Finnish.

The neutral and idiomatic word order is:

Uutiskirjeen otsikko on selkeä.

Some notes:

The genitive (owner) usually comes directly before the noun it owns:
- uutiskirjeen otsikko (newsletter’s title)
Putting uutiskirjeen at the end (Otsikko on selkeä uutiskirjeen) sounds ungrammatical or at least very odd.
Otsikko uutiskirjeen on selkeä is also incorrect in standard Finnish; you’d only get something remotely similar in very marked, poetic, or archaic styles, and even then it would be strange.

So for normal speech and writing, stick to: Uutiskirjeen otsikko on selkeä.

Why is there no word for “the” or “a” in this Finnish sentence?

Finnish has no articles (no words corresponding to “a/an” or “the”).

Definiteness or indefiniteness is usually understood from:

context
word order
specificity of the noun phrase

Uutiskirjeen otsikko on selkeä can be translated depending on context as:

“The newsletter’s title is clear.”
“The title of the newsletter is clear.”

In most realistic contexts, you’d translate it with “the” in English, but in Finnish you simply don’t mark that with a separate word.

How is Uutiskirjeen otsikko on selkeä pronounced, especially the long vowels and syllable stress?

Pronunciation guidelines:

Syllable division:

Uu-tis-kir-je-en ot-sik-ko on sel-ke-ä

Main points:

Primary stress is always on the first syllable of each word:
- UUTIS-kir-jeen OT-sik-ko on SEL-ke-ä
uu in uutis- is a long vowel, like holding the “oo” in English “food” longer.
-jeen has a long ee sound; the written -een here indicates length: [eːn].
Double consonants, like tt, kk, etc., are geminated: you hold them slightly longer, but here there’s kk in otsikko (ot-sik-ko), pronounced with a longer “k” sound between syllables.
Every written vowel is pronounced; ä is like the a in “cat” or “bad.”

So roughly (in a simplified English-like approximation):
[UU-tis-keer-yehn OT-sik-ko on SEL-ke-ae], with clear, even vowels and stress on first syllables.

How would this sentence change in the plural, for example “The titles of the newsletters are clear”?

You’d need to pluralize both uutiskirje and otsikko, and usually also adjust the adjective:

Uutiskirjeiden otsikot ovat selkeitä.

Breakdown:

uutiskirjeiden – plural genitive of uutiskirje = of the newsletters
otsikot – plural nominative of otsikko = titles
ovat – 3rd person plural of olla = are
selkeitä – partitive plural of selkeä = clear

In the plural, a very common pattern is:

[Plural subject] + ovat + [adjective in partitive plural]

because you’re describing a quality of several items.