På hennes profil finns ett gammalt inlägg om sommaren vid sjön.

Because Swedish follows the V2 rule in main clauses: the finite verb must come in the second position.

Here, På hennes profil is placed first for emphasis or as the starting point of the sentence. Once that happens, the verb finns has to come next:

• På hennes profil = first element
• finns = second element
• ett gammalt inlägg om sommaren vid sjön = the rest

A more basic order would be:

• Ett gammalt inlägg om sommaren vid sjön finns på hennes profil.

That is grammatical, but På hennes profil finns... sounds very natural when introducing something that is located somewhere.

Finns is the present tense of finnas, which means to exist / to be found / there is / there are.

In this sentence, finns means something like:

• there is
• can be found
• is there

So:

• På hennes profil finns ett gammalt inlägg... = On her profile, there is an old post...

Swedish uses finns when talking about the existence or presence of something.
Är means is/are, but it is used differently. Compare:

• Det finns ett inlägg på hennes profil. = There is a post on her profile.
• Inlägget är gammalt. = The post is old.

So finns introduces that something exists somewhere, while är describes it.

Because inlägg is an ett-word in Swedish.

Swedish nouns have two grammatical genders:

• en-words
• ett-words

Inlägg is neuter, so it takes:

• ett inlägg = a post

When an adjective describes an ett-word in the indefinite singular, the adjective usually gets -t:

• gammal → gammalt

So:

• ett gammalt inlägg = an old post

If the noun were an en-word, you would use:

• en gammal ...

For example:

• en gammal bok = an old book

This is adjective agreement.

In Swedish, adjectives change form depending on the noun they describe. For the indefinite singular:

• with an en-word: gammal
• with an ett-word: gammalt

Since inlägg is an ett-word, the adjective becomes:

• ett gammalt inlägg

You can compare:

• en gammal profil
• ett gammalt inlägg

This -t ending is very common with ett-words.

Because Swedish normally does not use an article together with a possessive word like min, din, hans, hennes, vår.

So you say:

• hennes profil = her profile
• min bok = my book
• deras hus = their house

Not:

• en hennes profil
• den hennes profilen

That would be wrong in standard Swedish.

So på hennes profil simply means on her profile.

På often means on, but in Swedish it is also used in some contexts where English might say on, in, or even something less literal.

With websites, social media pages, profiles, and platforms, Swedish often uses på:

• på Facebook
• på hennes profil
• på sidan = on the page

So på hennes profil is the natural way to say on her profile.

Here, om means about.

So:

• ett gammalt inlägg om sommaren = an old post about the summer

The preposition om is very commonly used for the topic of something:

• en bok om historia = a book about history
• en film om kriget = a film about the war
• ett inlägg om sommaren = a post about the summer

Be careful, though: om can have other meanings in other contexts, such as if. But here it clearly means about.

Sommaren is the definite form of sommar:

• en sommar = a summer
• sommaren = the summer

In this sentence, the speaker is referring to the summer as a specific idea or period, not just summer in a vague general sense.

So:

• om sommaren = about the summer

This sounds natural when talking about a particular summer or the summer season as a known topic.

Vid usually means by, near, or beside.

So:

• vid sjön = by the lake / near the lake

This suggests location next to the lake, not in it and not on top of it.

Compare:

• vid sjön = by the lake
• i sjön = in the lake
• på sjön = on the lake

So om sommaren vid sjön means something like about the summer by the lake.

Because sjön is the definite form of sjö:

• en sjö = a lake
• sjön = the lake

Swedish often uses the definite form when referring to a place that is understood or specific in the context.

So:

• vid sjön = by the lake

This is a very common pattern in Swedish. The definite ending is attached directly to the noun.

Yes, absolutely.

You could say:

• Det finns ett gammalt inlägg på hennes profil om sommaren vid sjön.

That also means There is an old post on her profile about the summer by the lake.

Using det finns is a very common way to express existence in Swedish.

The original sentence without det sounds a bit more literary or descriptive because it starts with the location:

• På hennes profil finns... = On her profile there is...

Both are correct; they just have slightly different style and focus.

Because hennes means her, referring to a specific female person, while sin is a reflexive possessive used when the possessor is the subject of the clause.

Here, there is no subject like hon in the sentence that owns the profile in a reflexive way. So Swedish uses:

• hennes profil = her profile

You would use sin in a sentence like:

• Hon skrev på sin profil. = She wrote on her own profile.

There, hon is the subject, and the profile belongs to that same person, so sin is required.

But in:

• På hennes profil finns...

the sentence just says on her profile, so hennes is correct.

It is singular.

You can tell because it has:

• ett = the singular indefinite article for an ett-word
• gammalt = singular adjective agreement for an ett-word

So:

• ett gammalt inlägg = one old post

The plural would be:

• inlägg = posts

Interestingly, inlägg has the same form in singular and plural, so the article and adjective help you see the difference. For example:

• ett gammalt inlägg = a/an old post
• gamla inlägg = old posts