Minilageret åpner i dag.

Because Norwegian usually puts the definite article at the end of the noun instead of using a separate word like the.

So:

• et minilager = a mini-storage unit / a self-storage facility
• minilageret = the mini-storage unit / the self-storage facility

The ending -et shows that the noun is:

• singular
• definite
• neuter gender

This is very common in Norwegian.

Because Norwegian normally writes compound nouns as one word.

So mini + lager becomes:

• minilager

Then the definite ending is added:

• minilageret

English often uses separate words where Norwegian prefers compounds, so this is something English speakers need to get used to.

Åpner is the present tense of the verb å åpne, which means to open.

Examples:

• å åpne = to open
• åpner = opens / is opening
• åpnet = opened

In this sentence, åpner is the finite verb.

Because Norwegian, like English, often uses the present tense for things that are happening now or are scheduled to happen very soon.

So åpner i dag can naturally mean:

• opens today
• is opening today

This is completely normal Norwegian.

I dag is the standard Norwegian expression for today.

Literally, i often means in, but you should learn i dag as a fixed time expression meaning today.

Other common time expressions with i include:

• i morgen = tomorrow
• i går = yesterday

So even though English does not say in day, Norwegian uses i dag.

It could be either, depending on context.

Two possibilities:

• It is just the first word in the sentence, so it is capitalized because it comes first.
• It is a name, such as a company or brand called Minilageret.

Norwegian capitalizes common nouns much less than English does, so capitalization here alone does not prove it is a proper name.

The basic order is:

• Minilageret = subject
• åpner = verb
• i dag = time expression

So the pattern is:

• Subject + Verb + Time expression

This is a very normal Norwegian sentence pattern.

Yes. Norwegian follows the verb-second rule in main clauses.

So if you begin with I dag, the verb still has to come second:

• I dag åpner minilageret.

Not:

• I dag minilageret åpner.

This is an important difference from English word order.

It is neuter, because the indefinite form would be:

• et minilager

That is why the definite form becomes:

• minilageret

In compounds, the gender usually comes from the last part of the word, called the head noun. Here the head is lager, so the whole compound follows that noun’s gender.

A simple learner-friendly pronunciation is roughly:

• OH-pner

A few helpful points:

• å sounds like a long o/aw sound.
• The p is usually heard, but the cluster pn may feel unusual for English speakers.
• The ending -er in many Norwegian verbs is often pronounced like a relaxed -er / -ər sound.

So åpner is not pronounced like English opener, even though it may look a little similar.

Yes. Norwegian present tense often covers both ideas.

So åpner can correspond to:

• opens
• is opening

The exact English translation depends on context. Norwegian does not always make the same distinction that English does between simple present and present progressive.

Because Norwegian usually marks definiteness with an ending on the noun itself.

So instead of saying something like the minilager, Norwegian says:

• minilageret

In some cases Norwegian can use both a separate determiner and a definite ending, but that usually happens with adjectives, for example:

• det nye minilageret = the new mini-storage facility

In your sentence, no separate word is needed.

Yes, but it means something slightly different in style.

• Minilageret åpner i dag = The mini-storage facility opens today
  This is the more natural, active way to say it.

• Minilageret åpnes i dag = The mini-storage facility is opened today / opens today
  This is more passive and can sound more formal or impersonal.

In everyday Norwegian, åpner is often the more natural choice.