Kauppakeskuksessa alkaa alennusmyynti perjantaina.

The ending -ssa / -ssä is the inessive case, which usually means “in / inside” a place.

• kauppa = shop
• keskus = center
• kauppakeskus = shopping center / mall
• kauppakeskuksessa = in the shopping center / in the mall

So kauppakeskuksessa literally means “in (the) shopping center”. Finnish uses case endings instead of separate prepositions like in.

Finnish has no articles (no separate words for “a / an / the”). Whether you translate it as “a” or “the” into English depends on the context, not on a special Finnish word.

• kauppakeskuksessa can be “in a shopping center” or “in the shopping center”.
• If the speaker and listener already know which mall they’re talking about, you’ll usually translate it as “in the shopping center”.
• If it’s mentioned for the first time, “in a shopping center” may be more natural in English.

The Finnish form itself doesn’t change; articles are an English problem, not a Finnish one.

The subject is alennusmyynti (“sale / discount sale”), even though it comes after the verb.

Structure of the sentence:

• Kauppakeskuksessa – adverbial of place (where?)
• alkaa – verb (starts / begins)
• alennusmyynti – subject (what starts?)
• perjantaina – adverbial of time (when?)

So in a more “English-style” order, it’s like saying:
Alennusmyynti alkaa kauppakeskuksessa perjantaina.
→ “The sale starts at/in the shopping center on Friday.”

Finnish word order is flexible; you can start with a location or time without changing who the subject is.

Because alennusmyynti is the subject and it’s a countable, whole event that’s starting. Subjects normally appear in the nominative singular when we talk about a complete, single thing:

• Alennusmyynti alkaa. – “The sale starts.”

Forms like:

• alennusmyyntiä (partitive) would suggest an ongoing, incomplete amount, which doesn’t fit with “starts” here.
• alennusmyynnin (genitive) would show possession or some other relation, not needed here.

So the basic form alennusmyynti is correct as the subject.

The verb agrees with the grammatical subject, not with the idea of how many items are on sale.

• alennusmyynti is singular (one sale event)
• therefore the verb is third person singular: alkaa

If the subject were plural, the verb would be plural:

• Alennusmyynnit alkavat perjantaina. – “The (various) sales start on Friday.”

In your sentence, you’re talking about one sale event, so alkaa is correct.

The ending -na / -nä is the adessive case in one of its uses: expressing “on (a day)”.

• perjantai = Friday
• perjantaina = on Friday

Finnish often uses the adessive for days:

• maanantaina – on Monday
• keskiviikkona – on Wednesday
• jouluna – at Christmas

So perjantaina is the natural way to say “on Friday.”

Yes, Finnish word order is quite flexible. The basic meaning stays the same, but the focus changes slightly.

1. Kauppakeskuksessa alkaa alennusmyynti perjantaina.
   – Focus on where: “At the shopping center, a sale starts on Friday.”

2. Alennusmyynti alkaa kauppakeskuksessa perjantaina.
   – Neutral, subject-first style: “The sale starts at the shopping center on Friday.”

3. Perjantaina alkaa alennusmyynti kauppakeskuksessa.
   – Focus on when: “On Friday, a sale starts at the shopping center.”

4. Perjantaina kauppakeskuksessa alkaa alennusmyynti.
   – Strong “scene-setting”: “On Friday, at the shopping center, a sale starts.”

All are grammatical; you choose based on what you want to emphasize first: place, event, or time.

Yes, you can, but the nuance is different.

• Kauppakeskuksessa alkaa alennusmyynti perjantaina.
  – Emphasizes the start.
  – “A sale starts at the shopping center on Friday.”

• Kauppakeskuksessa on alennusmyynti perjantaina.
  – Emphasizes existence/occurrence on that day.
  – “There is a sale at the shopping center on Friday.”

Use alkaa when you care about the beginning of the sale.
Use on when you just want to say that on Friday, the sale is happening.

Literally:

• alennus = discount
• myynti = selling / sale
• alennusmyynti = discount sale, clearance sale

Spoken and written Finnish also often uses:

• ale – very common, short form
  
  • Kauppakeskuksessa alkaa ale perjantaina.
• tarjous – “special offer” (not exactly the same, but related)

Alennusmyynti is a bit more formal/neutral; ale is very common in everyday language and in ads.

Both are understood, but kauppakeskus is more standard/common for shopping mall / shopping center.

• kauppa = shop, store
• kauppakeskus = shopping center / mall
• ostos = purchase, shopping
• ostoskeskus = theoretically “shopping center”, but is less common in modern usage

Most Finns will say kauppakeskus. So kauppakeskuksessa alkaa alennusmyynti perjantaina sounds more natural than using ostoskeskus.

You can label each part by its function and case:

• Kauppakeskus-ssa

  • kauppakeskus = shopping center
  • -ssa = inessive (in)
  • role: place adverbial (where?)

• alkaa

  • verb, 3rd person singular present (starts)

• alennus-myynti

  • alennus = discount
  • myynti = selling / sale
  • nominative singular
  • role: subject (what starts?)

• perjantai-na

  • perjantai = Friday
  • -na = adessive (here: on (a day))
  • role: time adverbial (when?)

So structurally:
[Place] [Verb] [Subject] [Time]
→ In the shopping center starts a sale on Friday. (more natural English: A sale starts in the shopping center on Friday.)