Hvis håret blir for langt, må jeg klippe det.

Hvis means if. It introduces a condition:

• Hvis håret blir for langt = If the hair gets too long

This is a conditional subordinate clause. In Norwegian, hvis is a very common way to say if when one thing depends on another.

Håret is the definite form of hår:

• hår = hair
• håret = the hair

In Norwegian, body parts are often expressed with the definite form when it is clear whose body part is meant. So håret here naturally means something like my hair or the hair, depending on context.

So:

• Hvis håret blir for langt
  literally: If the hair gets too long
  naturally: If my hair gets too long

Using just hår here would sound wrong in normal Norwegian.

Blir is from bli, which means become or get.

So:

• blir for langt = gets too long / becomes too long
• er for langt = is too long

The sentence uses blir because it is talking about a change of state: the hair is not too long yet, but it may become too long.

Compare:

• Håret er for langt. = The hair is too long.
• Håret blir for langt. = The hair gets too long.

Here for means too.

So:

• langt = long
• for langt = too long

This is a very common pattern in Norwegian:

• for dyrt = too expensive
• for sent = too late
• for vanskelig = too difficult

English speakers sometimes confuse this with English for, but in this sentence it does not mean for in the English sense.

Langt is the form of lang used here because it agrees with håret, which is a neuter noun.

• en lang bil = a long car
• et langt hår? not normally said this way as a mass noun phrase, but the adjective form would still be langt with a neuter noun
• håret er langt = the hair is long

Since hår / håret is neuter, the adjective appears as langt.

This is because of Norwegian word order.

The sentence begins with a subordinate clause:

• Hvis håret blir for langt

When a main clause comes after something placed first, Norwegian usually follows the verb-second (V2) rule. That means the finite verb comes before the subject in the main clause:

• Hvis håret blir for langt, må jeg klippe det.

Literally, the second clause is ordered like:

• must I cut it

but in natural English we say:

• I have to cut it

If the main clause stood alone, it would be:

• Jeg må klippe det.

So the word order changes because the if-clause comes first.

Because hår is a neuter noun, so the pronoun referring back to it is det.

• en-words often take den
• et-words often take det

Since we have:

• håret = neuter

the correct pronoun is:

• det = it

So:

• må jeg klippe det = I have to cut it

Må is the present tense of måtte, and here it means must or have to.

In English, must can sound strong or formal, so have to is often the most natural translation here:

• må jeg klippe det = I have to cut it

So yes, must is possible, but have to often sounds better in everyday English.

Not necessarily. Klippe det simply means cut it.

So the sentence says that if the hair gets too long, it needs to be cut. It does not by itself tell you whether:

• you cut it yourself
• someone else cuts it
• you go to a hairdresser

Context decides that.

A related expression is å klippe seg, which often means to get a haircut / have one’s hair cut. That can sound more idiomatic in some situations, but it is not exactly the same grammatical structure as klippe det.

Yes. Norwegian often uses the present tense for things that are generally true, repeated, or expected in the future.

So:

• Hvis håret blir for langt, må jeg klippe det.

is in the present tense, but it means something like:

• If my hair gets too long, I have to cut it
• If my hair becomes too long, I’ll have to cut it

This is very normal in Norwegian and also quite natural in English.

Word-for-word, the Norwegian order may look a bit like that, but that is not the correct natural English translation.

Because of Norwegian word order after the opening clause, må jeg does not mean the speaker is asking a question. It is still a statement:

• Hvis håret blir for langt, må jeg klippe det.
• If my hair gets too long, I have to cut it.

So even though the order is må jeg, the whole sentence is not a question.