Filterrensen begynner i dag.

Because Norwegian normally writes compound nouns as a single word.

So filterrensen is built from:

• filter = filter
• rens = cleaning / cleanse
• -en = the definite ending

English often uses several words where Norwegian prefers one compound word.

The ending -en is the definite article attached to the noun. In English, you usually put the before the noun; in Norwegian, it is often added to the end instead.

So:

• filterrens = filter cleaning / a filter cleaning
• filterrensen = the filter cleaning

That is why there is no separate word for the here.

Because the compound joins filter and rens.

• filter ends in r
• rens begins with r

When they are combined, both letters stay, so you get rr:

• filter
  • rens
    • -en → filterrensen

It is a noun here, and it is the subject of the sentence.

The verb is begynner.

So the structure is:

• Filterrensen = subject
• begynner = verb
• i dag = time expression

Begynner is the present tense of the verb å begynne.

• å begynne = to begin
• begynner = begin / begins / is beginning, depending on context

In this sentence, it means begins.

No. Norwegian verbs do not change for person the way English verbs sometimes do.

So you get:

• jeg begynner = I begin
• du begynner = you begin
• han begynner = he begins
• vi begynner = we begin

The verb form stays the same.

Norwegian commonly uses the expression i dag for today.

It is a fixed time expression:

• i dag = today

Even though i often means in, you should learn i dag as a set phrase.

Yes, absolutely.

Both are correct:

• Filterrensen begynner i dag.
• I dag begynner filterrensen.

The difference is mainly emphasis:

• Filterrensen begynner i dag. focuses first on the filter cleaning
• I dag begynner filterrensen. focuses first on today

Notice that when i dag comes first, the verb still has to stay in second position:

• I dag begynner filterrensen not
• I dag filterrensen begynner

This is a very important Norwegian word-order rule.

Yes. Norwegian often uses the present tense for things happening now or starting at a scheduled or clear time.

So begynner i dag is completely normal Norwegian.

English can do something similar:

• The course starts today
• The train leaves tomorrow

So the Norwegian present tense here feels very natural.

A rough guide is beh-GYNN-er, but the y sound is not a normal English sound.

For y in Norwegian:

• say something like ee
• but round your lips as if you were saying oo

Also:

• the g is a hard g
• the nn is pronounced clearly

So begynner is roughly beh-GYNN-er, with a rounded vowel in the stressed syllable.

Often yes.

• begynner = begins / starts
• starter = starts

In many everyday contexts, both can work. Begynner is a very standard choice, and it often sounds a little more neutral. Starter is also common, especially in spoken language.

So a sentence like Filterrensen starter i dag could also be possible, depending on context.