Han reiser til fronten.

Because reiser is the present tense form of the verb å reise (to travel / to go on a journey).

• å reise = infinitive
• reiser = present tense

Norwegian main clauses normally need a finite verb, just like English:

• Han reiser ... = He travels / He is traveling / He is going ...

Unlike English, Norwegian does not add different verb endings for I/you/he/we/they. The same present-tense form is used for all subjects:

• Jeg reiser
• Du reiser
• Han reiser
• Vi reiser

It can often mean future time in Norwegian, depending on context.

The present tense is very commonly used for planned or expected future actions:

• Han reiser til fronten i morgen. = He is going to the front tomorrow.

So even without a future marker, Han reiser til fronten can easily be understood as He is going to the front rather than only He travels to the front.

This is very natural in Norwegian and works a lot like English sentences such as:

• He leaves tomorrow.
• She starts next week.

Til usually means to, and it is used for movement toward a destination.

So:

• reise til = travel to
• gå til = go to / walk to
• komme til = come to

In this sentence, the person is moving toward the front, so til is the natural choice.

A useful contrast is:

• Han reiser til fronten. = He goes to the front.
• Han er ved/på fronten. = He is at the front.

So til focuses on the destination, not the location where he already is.

Because fronten is the definite singular form of the noun front.

In Norwegian, nouns often add the definite article as an ending, instead of using a separate word like the.

• en front = a front
• fronten = the front

So the -en ending here means the.

This is one of the most important features of Norwegian nouns:

• en bil = a car
• bilen = the car
• en front = a front
• fronten = the front

In this kind of sentence, fronten usually means the front in a military sense — the battlefront or front line area.

Even though English often says the front lines, Norwegian commonly uses the singular form:

• fronten = the front / the front line / the war front

The exact nuance depends on context, but it normally suggests a war setting rather than just the physical front side of something.

Yes. Han drar til fronten is also natural.

Both å reise and å dra can mean to go / to travel, but they are not always identical in feel:

• å reise often sounds a bit more like travel / make a journey
• å dra is very common in everyday speech for go / leave

So:

• Han reiser til fronten = slightly more formal or neutral
• Han drar til fronten = very natural in everyday spoken Norwegian

In many contexts, either one works.

This is the normal Norwegian main clause word order:

Subject + verb + other elements

So:

• Han = subject
• reiser = verb
• til fronten = prepositional phrase

That gives:

• Han reiser til fronten.

This is the same basic order as in English:

• He goes to the front.

A very important thing in Norwegian is that the verb is usually in second position in main clauses. In a simple sentence like this, that naturally gives subject + verb.

Only because it is the first word of the sentence.

Norwegian does not capitalize pronouns like English used to in older styles, and it does not capitalize nouns the way German does.

So:

• Han reiser til fronten.
• Jeg så ham i går.
• fronten er farlig.

Only the start of the sentence and proper names get capitals.

A careful approximation is:

• reiser ≈ RYE-ser

But that is only an approximation for English speakers.

A few helpful notes:

• the r is Norwegian, not an English r
• ei in reise sounds roughly like the vowel in English eye
• the final -er is usually a light, unstressed ending

So the whole sentence is roughly:

• Han RYE-ser til FRON-ten

Also, in natural speech, han is often pronounced weaker than the spelling suggests.

Yes. Norwegian present tense often covers several meanings that English separates:

• travels
• is traveling
• sometimes even is going to travel

So reiser does not by itself force one exact English tense choice. The context decides.

For example:

• Han reiser ofte. = He travels often.
• Han reiser nå. = He is traveling now / He is leaving now.
• Han reiser i morgen. = He is traveling tomorrow / He is leaving tomorrow.

This is completely normal in Norwegian.

Yes, but it changes the meaning.

• til fronten = to the front (movement toward it)
• på fronten = at/on the front (location, being there)

So compare:

• Han reiser til fronten. = He is going to the front.
• Han kjemper på fronten. = He is fighting at the front.

This is an important preposition difference in Norwegian: one form for going somewhere, another for being somewhere.