Tavarat ovat laatikossa.

Because tavarat is the plural form of tavara.

• tavara = an item, a thing, goods, stuff
• tavarat = the items, the things, the goods

In this sentence, the subject is plural, so Finnish uses the plural verb form too: ovat.

Ovat is the 3rd person plural form of the verb olla = to be.

A quick comparison:

• on = is
• ovat = are

So:

• Tavara on laatikossa = The item is in the box.
• Tavarat ovat laatikossa = The items are in the box.

In standard written Finnish, the verb agrees with the subject in number, just like in English here.

The ending -ssa is the inessive case, which usually means in or inside.

So:

• laatikko = box
• laatikossa = in the box

This is very common in Finnish. Instead of using a separate word like in, Finnish often adds a case ending to the noun itself.

Other examples:

• talossa = in the house
• autossa = in the car
• kirjassa = in the book

This happens because of consonant gradation, a very common sound change in Finnish.

The basic form is:

• laatikko

But when certain endings are added, the kk often becomes k:

• laatikko
• laatikossa

So the stem changes slightly before the case ending is added.

This kind of change happens in many Finnish words, for example:

• kukka → kukassa
• matto → matossa

It is something learners usually just have to get used to by seeing many examples.

Finnish does not have articles like a, an, or the.

So laatikossa can mean:

• in the box
• in a box

and tavarat can mean something like:

• the items
• the things
• the goods

Which one sounds best depends on context. In many situations, context makes it clear whether something is definite or indefinite.

Tavarat is in the nominative plural.

That means it is the basic plural form used here as the subject of the sentence.

Breakdown:

• tavara = singular nominative
• tavarat = plural nominative

Since tavarat is the subject, nominative is the expected case here.

Because this sentence is talking about a specific, complete set of items as the subject: the items are in the box.

The nominative plural tavarat suggests a definite group.

If you wanted to say something more like there are some items in the box, Finnish would more naturally use an existential structure with the partitive:

• Laatikossa on tavaroita.

That means something like There are some items in the box.

So the difference is roughly:

• Tavarat ovat laatikossa. = The items are in the box.
• Laatikossa on tavaroita. = There are some items in the box.

This is an important distinction in Finnish.

The neutral, ordinary word order here is:

Tavarat ovat laatikossa.
subject + verb + location

Finnish word order is more flexible than English word order, but changing it usually changes the emphasis.

For example, starting with laatikossa can put more focus on the location:

• Laatikossa ovat tavarat.

That is possible, but it sounds more marked or stylistically special than the basic version.

For learners, Tavarat ovat laatikossa is the safest and most natural neutral order.

Usually yes. The inessive ending -ssa / -ssä means being in or inside something.

So laatikossa strongly suggests that the items are inside the box, not on top of it or near it.

Compare:

• laatikossa = in the box
• laatikon päällä = on top of the box
• laatikon vieressä = next to the box

Finnish is often very precise about location.

This is because of vowel harmony.

Finnish endings often come in two versions:

• -ssa
• -ssä

Words with back vowels such as a, o, u usually take -ssa.
Words with front vowels such as ä, ö, y usually take -ssä.

Since laatikko contains the back vowels a and o, the correct form is:

• laatikossa

A front-vowel example:

• kylä → kylässä = in the village

A simple pronunciation guide:

• Tavarat → TA-va-rat
• ovat → O-vat
• laatikossa → LAA-ti-kos-sa

A few useful points:

• Finnish stress usually falls on the first syllable.
• aa is a long vowel, so laa- is held a bit longer.
• ss is a long consonant, so the s sound in -ssa is also a bit longer.

So the rhythm is something like:

TAvarat OVAT LAA tikos sa

Yes. Tavara / tavarat is a fairly broad word.

Depending on context, tavarat can mean:

• things
• items
• stuff
• goods
• belongings

For example:

• in a shop context, it may sound like goods or items
• in a home context, it may sound like things or belongings

So the exact English translation depends on what kind of tavarat you are talking about.

In colloquial spoken Finnish, you may hear forms that do not match standard written grammar exactly. In everyday speech, many speakers use on very broadly.

But in standard Finnish, the correct form is:

• Tavarat ovat laatikossa.

So for learning grammar and for writing, you should use ovat with a plural subject like tavarat.