De vil oppnå målet.

Because De is the first word of the sentence, it has to be capitalized anyway. So in this sentence, the capital D by itself does not tell you whether it means they or the formal you.

Only the context, or the translation you were given, tells you which meaning is intended.

A useful rule:

• de = they
• De = formal/polite you in very formal writing

But at the start of a sentence, both look like De, so you need context.

Not very common. As a polite form of you, De sounds very formal, old-fashioned, or sometimes like customer-service language.

In everyday modern Norwegian, people usually say:

• du = you singular
• dere = you plural

So if De here means formal you, that is possible, but it is not the most typical everyday usage. If it means they, then it is completely normal.

Vil is the present tense of ville.

It can express:

• wish / desire / intention → want to
• future meaning → will

So De vil oppnå målet can, depending on context, mean something like:

• They want to achieve the goal
• They will achieve the goal

Since the meaning has already been given to you, follow that meaning here. The important thing is that vil is a flexible word, and context decides the best English translation.

Because vil is a modal verb, and after modal verbs Norwegian uses the bare infinitive.

So you get:

• vil oppnå
• kan komme
• må gå
• skal arbeide

Not:

• vil å oppnå

This is very similar to English, where you say will achieve, not will to achieve.

Oppnå is the infinitive form of the verb, meaning to achieve, to attain, or to accomplish.

In this sentence it comes after vil, so it stays in the infinitive:

• vil oppnå

It is also written as one word: oppnå.

Because målet is the definite form.

• mål = goal
• målet = the goal

Unlike English, Norwegian often puts the definite article at the end of the noun instead of using a separate word like the.

So:

• et mål = a goal
• målet = the goal

Since mål is a neuter noun, the singular definite ending is typically -et.

Because Norwegian usually attaches definiteness directly to the noun.

So instead of saying something like the goal with a separate article, Norwegian says:

• målet

This is a very common feature of Scandinavian languages.

Compare:

• en bil = a car
• bilen = the car
• et hus = a house
• huset = the house
• et mål = a goal
• målet = the goal

This is the normal word order for a simple main clause:

• De = subject
• vil = finite verb
• oppnå = infinitive
• målet = object

Norwegian follows the V2 rule in main clauses, which means the finite verb normally comes in the second position.

Here, the subject comes first, so the finite verb vil comes second:

• De vil oppnå målet

If another element came first, the finite verb would still stay second:

• Snart vil de oppnå målet.
• I morgen vil de oppnå målet.

Yes. Norwegian has several ways to express future meaning or intention.

For example:

• De vil oppnå målet
  Can suggest intention, willingness, or future meaning depending on context.

• De kommer til å oppnå målet
  A very clear future prediction: They are going to achieve the goal.

• De skal oppnå målet
  Can sound like a plan, an instruction, or something expected/required.

So the original sentence is perfectly natural, but the exact nuance depends on why the speaker chose vil.

A rough pronunciation for an English speaker is:

• oppnå ≈ OP-noh
• målet ≈ MOH-le

A few helpful notes:

• å has a vowel sound somewhat like the vowel in British more, though not exactly the same.
• In many everyday pronunciations, the final -t in målet is weak or silent.
• Norwegian pronunciation varies a lot by dialect, so exact pronunciation can differ.

If you want a simple learner-friendly version, OP-noh MOH-le is a reasonable start.