Elokuussa uusi lukujärjestys tulee sähköpostiin, ja tarkistan sen heti.

Elokuussa is the inessive form of elokuu (August). The ending -ssa / -ssä often means in.

So:

• elokuu = August
• elokuussa = in August

Finnish usually expresses months this way:

• tammikuussa = in January
• kesäkuussa = in June
• elokuussa = in August

So Elokuussa is a time expression meaning in August.

Finnish word order is flexible, and the beginning of the sentence often gives the topic or setting first.

By starting with Elokuussa, the speaker sets the time frame right away: In August...

A more neutral alternative would also be possible:

• Uusi lukujärjestys tulee sähköpostiin elokuussa.

Both are correct, but putting Elokuussa first feels natural when the time is important background information.

Finnish very often uses the present tense for future events when the time is clear from context.

Here, the future meaning is already shown by Elokuussa, so Finnish does not need a separate future tense.

• tulee = comes / will come / arrives
• Elokuussa ... tulee = in August ... will arrive

This is completely normal Finnish.

Tulee is the 3rd person singular form of tulla, which basically means to come.

In this sentence, it is best understood as:

• arrives
• comes
• is sent / comes in

So uusi lukujärjestys tulee sähköpostiin means something like the new schedule arrives by email / comes to the email inbox.

Finnish often uses tulla in places where English would say arrive.

Because it is the subject of the first clause.

• uusi = new
• lukujärjestys = timetable / schedule
• uusi lukujärjestys = the new schedule

Subjects are often in the nominative, which is the basic dictionary form.

Here, uusi lukujärjestys is the thing that comes / arrives, so it stays in the nominative.

Yes, lukujärjestys is a compound word.

It means timetable, schedule, or in a school context often class schedule.

It is made from:

• luku
• järjestys = order / arrangement

As a whole, though, you should learn lukujärjestys as one common word meaning schedule/timetable, especially for school or studies.

Sähköpostiin is the illative form of sähköposti.

The illative often means into, to, or movement toward something.

So:

• sähköposti = email
• sähköpostiin = into the email / to the email inbox

In natural English, we usually would not say into the email, but Finnish does. In context, it means that the schedule arrives by email or in the email inbox.

Good question. Finnish often leaves possession unspoken when it is obvious from context.

So sähköpostiin can naturally mean something like:

• to the email inbox
• to my email, if that is understood

If the speaker wants to be more explicit, they could say:

• sähköpostiini = into my email
• minun sähköpostiini = into my email

But in many everyday sentences, the shorter sähköpostiin is perfectly natural.

Because ja is joining two clauses, and those clauses have different subjects.

The two parts are:

• Elokuussa uusi lukujärjestys tulee sähköpostiin
• ja tarkistan sen heti

In the first clause, the subject is uusi lukujärjestys.
In the second clause, the subject is understood as I, from tarkistan.

Because the subjects are different, Finnish normally uses a comma before ja here.

Because the verb ending already shows the subject.

Tarkistan means I check.

The ending -n tells you it is 1st person singular, so Finnish usually does not need minä.

• tarkistan = I check
• minä tarkistan = I check

Both are possible, but the version without minä is more normal unless the speaker wants extra emphasis.

Because sen is the object form here.

• se = it, as a subject form
• sen = it, as an object form in this kind of sentence

In tarkistan sen heti, the speaker is doing the action to it — checking it — so Finnish uses sen.

This is very common:

• Näen sen. = I see it.
• Ostan sen. = I buy it.
• Tarkistan sen. = I check it.

So sen refers back to uusi lukujärjestys.

Heti means immediately or right away.

In Finnish, adverbs like this are quite flexible in position, but tarkistan sen heti is a very natural order.

It puts the action first and the time emphasis after it:

• tarkistan sen heti = I check it immediately

You could move heti in some contexts, but this version sounds smooth and standard.

Yes. Finnish allows some word-order variation, although the nuance may change slightly.

For example:

• Uusi lukujärjestys tulee sähköpostiin elokuussa, ja tarkistan sen heti.
• Elokuussa uusi lukujärjestys tulee sähköpostiin ja tarkistan sen heti.

The original sentence is very natural because:

• Elokuussa sets the time first
• the comma clearly separates the two clauses
• sen heti sounds natural after tarkistan

So the original is a good, idiomatic sentence.