Laavu on järven lähellä.

Finnish does not have articles like English a/an and the.

So laavu can mean either:

• a shelter
• the shelter

The exact meaning comes from context. If the listener already knows which shelter you mean, English usually uses the. Finnish still just says laavu.

On is the third-person singular present form of olla, which means to be.

So here:

• laavu on = the shelter is

Because laavu is singular, the verb is on.

Because lähellä in this sentence is used as a postposition, and the noun before it usually goes into the genitive.

So:

• järvi = lake (basic dictionary form, nominative)
• järven = of the lake / lake's (genitive form)

In järven lähellä, the genitive does not mean possession in the normal English sense. It is just the form required by this structure.

That is part of the noun’s normal inflection pattern.

Järvi belongs to a group of Finnish nouns where the final -i changes to -e- before many endings. So the stem becomes järve-.

For example:

• järvi = lake
• järven = of the lake
• järveä = lake (partitive)
• järvessä = in the lake

So järven is the regular genitive form, not järvin.

Because Finnish often uses postpositions, which come after the noun, instead of prepositions, which come before it.

So English:

• near the lake

becomes Finnish:

• järven lähellä

This is a very common Finnish pattern: noun + postposition.

Also, with some words, Finnish can sometimes use a preposition-like structure too. For lähellä, you may also hear lähellä järveä. But your sentence uses the very common postpositional pattern järven lähellä.

Not really, even though järven is a genitive form.

The genitive in Finnish often marks possession, but it is also used with many postpositions. In this sentence, järven lähellä simply means near the lake.

So you should understand it as a location phrase, not as real ownership.

Yes. Finnish word order is more flexible than English word order.

Your sentence:

• Laavu on järven lähellä.

is a neutral way to say that the shelter is near the lake.

You could also say:

• Järven lähellä on laavu.

That puts more focus on the location, as if answering:

• What is near the lake?

So the meaning stays very similar, but the emphasis changes.

In this sentence, it is best to treat lähellä as a separate word meaning near / nearby.

It does look like a word with the ending -llä, which is also a Finnish case ending in other contexts, but here lähellä functions as an adposition or adverb-like word. For a learner, the practical thing is:

• learn lähellä as a whole word
• learn that it often goes with a noun in the genitive: järven lähellä

A rough guide for an English speaker:

• laavu ≈ LAA-vu
  
  • the aa is long
• on ≈ on
• järven ≈ YAR-ven, but with ä pronounced more to the front of the mouth than English a
• lähellä ≈ LA-hel-lä, with the ll held a little longer

A few useful pronunciation points:

• j in Finnish sounds like English y in yes
• ä is somewhat like the vowel in cat, but cleaner and shorter
• double consonants, like ll, are pronounced longer than single ones
• Finnish pronunciation is usually very regular: words are mostly said the way they are spelled

A simple approximate pronunciation of the whole sentence is:

• LAA-vu on YAR-ven LA-hel-lä