Toukokuussa koeviikko tulee juuri ennen kesälomaa, joten monet opiskelijat ovat väsyneitä.

Toukokuussa means in May.

The base word is toukokuu = May.
The ending -ssa is the inessive case, which often means in.

With months, Finnish commonly uses this case to express time:

• tammikuussa = in January
• helmikuussa = in February
• toukokuussa = in May

So Toukokuussa literally means in May.

Koeviikko is a compound word:

• koe = test, exam
• viikko = week

So koeviikko means exam week or test week.

Finnish makes a lot of compound words like this, and they are usually written as one word.

Yes, tulee literally means comes, from the verb tulla = to come.

In this sentence, koeviikko tulee juuri ennen kesälomaa means something like:

• exam week comes just before summer vacation
• more naturally in English: exam week is just before summer vacation or exam week takes place just before summer vacation

Finnish often uses tulla in time-related expressions where English might prefer be, happen, or take place.

Juuri ennen means just before or right before.

• juuri = just, exactly, right
• ennen = before

So:

• juuri ennen kesälomaa = just before summer vacation

This is a very common expression in Finnish.

Because ennen normally takes the partitive case.

The basic form is:

• kesäloma = summer vacation / summer holiday

After ennen, it becomes:

• ennen kesälomaa = before summer vacation

So the -a / -ä ending here is partitive singular.

Other examples:

• ennen koulua = before school
• ennen ruokaa = before food / before the meal
• ennen juhlaa = before the party

Joten means so, therefore, or as a result.

It introduces a consequence:

• koeviikko tulee juuri ennen kesälomaa = exam week comes just before summer vacation
• joten monet opiskelijat ovat väsyneitä = so many students are tired

A useful contrast:

• koska = because
• joten = so / therefore

So joten points forward to the result.

Monet opiskelijat means many students.

• moni = many a / many
• plural form monet = many
• opiskelijat = students

This is a normal way to talk about a countable plural group.

Compare:

• monet opiskelijat = many students
• paljon opiskelijoita = a lot of students

Both can be possible in some contexts, but monet opiskelijat is very natural here.

Because it is the subject of the clause:

• monet opiskelijat ovat väsyneitä = many students are tired

The basic singular is:

• opiskelija = student

The nominative plural is:

• opiskelijat = students

Since the subject is plural, the verb is also plural:

• ovat = are

Because the subject is plural.

• on = is
• ovat = are

Here the subject is monet opiskelijat = many students, which is plural, so Finnish uses the plural verb:

• Monet opiskelijat ovat väsyneitä.

If the subject were singular, you would use on:

• Opiskelija on väsynyt. = The student is tired.

Väsyneitä is the partitive plural of väsynyt = tired.

In Finnish, when a plural subject is described with an adjective after olla (to be), the adjective is very often in the partitive plural when it expresses a general state or quality:

• Opiskelijat ovat väsyneitä. = The students are tired.
• Lapset ovat iloisia. = The children are happy.

So monet opiskelijat ovat väsyneitä is a very natural standard way to say many students are tired.

Finnish word order is fairly flexible, and the beginning of the sentence often shows the time, topic, or context first.

So Toukokuussa at the front means the sentence is framed as:

• In May, ...

This is very natural in Finnish. It helps set the time immediately.

You could move elements around in some contexts, but this order is clear and common.

Because Finnish has no articles.

English uses:

• a
• an
• the

Finnish does not. So words like koeviikko, kesäloma, and opiskelijat appear without articles.

The exact English meaning depends on context:

• koeviikko can mean an exam week, the exam week, or just exam week
• opiskelijat can mean students or the students, depending on context

You learn this from the situation rather than from an article word.