Han velger motsatt side.

• Han = he
• velger = chooses / is choosing
• motsatt = opposite
• side = side

So the sentence has the very common pattern subject + verb + object, just like English:

Han + velger + motsatt side

The base form is å velge, meaning to choose.

Here, velger is the present tense form:

• å velge = to choose
• velger = chooses / is choosing
• valgte = chose
• har valgt = has chosen

A useful point for English speakers: Norwegian verbs do not change according to the subject the way English verbs sometimes do. You say:

• jeg velger
• du velger
• han velger
• vi velger

The verb form stays the same.

Because motsatt is an adjective, and adjectives normally come before the noun in Norwegian, just as in English.

So:

• motsatt side = opposite side
• not side motsatt

This is the normal noun phrase order:

• en stor bil = a big car
• et gammelt hus = an old house
• motsatt side = opposite side

This is a very natural question, because English usually wants the opposite side or an opposite side.

In Norwegian, a bare noun phrase can sometimes appear after certain verbs, especially when the meaning is a bit general or idiomatic. So Han velger motsatt side is understandable as He chooses the opposite side.

However, if you mean a specific side, many speakers would often prefer:

Han velger den motsatte siden.

That version is more explicitly the opposite side.

So the difference is roughly:

• motsatt side = more general / somewhat bare / concise
• den motsatte siden = a specific, clearly identified opposite side

Side is the indefinite form of the noun.
Siden is the definite form, meaning the side.

Compare:

• en side = a side
• siden = the side

Norwegian often marks definiteness by adding an ending to the noun. So if you say:

den motsatte siden

you get both:

• den to mark the definite adjective phrase
• siden as the definite form of side

That is a very common Norwegian pattern.

Yes, here motsatt is an adjective describing side.

A form you will often see is:

• motsatt in indefinite singular contexts
• motsatte in definite and plural contexts

For example:

• den motsatte siden = the opposite side
• motsatte synspunkter = opposite points of view

So in your sentence, motsatt is simply the adjective modifying side.

It can be either, depending on context.

It might mean:

• a literal side, like one side of a room, road, or object
• a figurative side, like a position in an argument, conflict, or debate

So side in Norwegian, like side in English, can be concrete or abstract.

To make it negative, put ikke after the verb:

Han velger ikke motsatt side.
= He does not choose the opposite side.

To make it a yes/no question, Norwegian usually puts the verb first:

Velger han motsatt side?
= Is he choosing the opposite side? / Does he choose the opposite side?

That word order is very common in Norwegian main-clause questions.

Yes. Norwegian follows the verb-second rule in main clauses. That means if you move another element to the front, the verb still stays in the second position.

Normal order: Han velger motsatt side.

With a time expression in front: I dag velger han motsatt side.
= Today he chooses the opposite side.

Notice that velger stays in second position, and han moves after it. This is an important difference from English.