Registreringen gjelder adresseendringen og adressesperren.

Because -en is the definite ending for many common-gender nouns in Norwegian.

• registrering = registration / registering
• registreringen = the registration

So Norwegian often puts the at the end of the noun instead of using a separate word before it.

In Norwegian, definiteness is usually built into the noun itself with an ending.

So:

• registrering = registration

• registreringen = the registration

• adresseendring = change of address / address change

• adresseendringen = the change of address

• adressesperre = address block / address protection
• adressesperren = the address block / the address protection

This is very normal in Norwegian. English uses a separate word (the), but Norwegian often uses a suffix instead.

Gjelder means something like:

• concerns
• applies to
• is about

So Registreringen gjelder adresseendringen og adressesperren means that the registration is connected to or concerns those two things.

A very common pattern is:

• Dette gjelder meg. = This concerns me / This applies to me.
• Regelen gjelder alle. = The rule applies to everyone.

Yes. Norwegian very often forms compound nouns, where English might use two words or a longer phrase.

Here:

• adresse + endring → adresseendring
• adresse + sperre → adressesperre

Then the definite ending is added:

• adresseendringen
• adressesperren

This is extremely common in Norwegian, and learners often need practice spotting where one compound begins and ends.

When Norwegian makes compound nouns, the first part is usually the base form of the noun, not necessarily a full standalone form with all the endings you might expect in English.

So:

• adresse
  • endring → adresseendring
• adresse
  • sperre → adressesperre

You just put the parts together. There is no extra word like of in between.

English often says:

• change of address

But Norwegian prefers the compound:

• adresseendring

The difference is indefinite vs definite:

• adresseendring = a change of address / change of address
• adresseendringen = the change of address

Likewise:

• adressesperre = an address block / address protection
• adressesperren = the address block / the address protection

So the sentence is talking about specific, known things, not just those things in general.

These nouns are common gender nouns, which is why they take -en in the definite singular.

Examples:

• en registrering → registreringen
• en adresseendring → adresseendringen
• en adressesperre → adressesperren

In Bokmål, many nouns are either:

• common gender (en)
• neuter (et)

Here, all the nouns in the sentence are common gender.

This is a normal Norwegian main-clause pattern:

• Subject + verb + rest

So:

• Registreringen = subject
• gjelder = verb
• adresseendringen og adressesperren = what it concerns

Norwegian is a V2 language, which means the finite verb is normally in the second position in main clauses. In this sentence, the subject comes first, so the order looks quite similar to English.

You usually would not use Registrering here if you mean the registration in a specific case.

Compare:

• Registrering gjelder adresseendring.
  = Registration concerns change of address.
  This sounds more general or headline-like.

• Registreringen gjelder adresseendringen og adressesperren.
  = The registration concerns the change of address and the address protection.
  This refers to a specific registration and specific items.

So the -en endings matter a lot.

Because the sentence is referring to specific, identifiable things:

• adresseendringen = the specific address change
• adressesperren = the specific address protection/block

If the meaning were more general, you might see the indefinite forms instead:

• Registreringen gjelder adresseendring og adressesperre.

But in your sentence, the writer is talking about particular things already known in the context.

In compounds, Norwegian usually puts the main stress on the first part of the compound.

So in:

• adresseendring
• adressesperre

the compound stress starts on adresse-, though the exact rhythm can vary naturally in speech.

Also note:

• gjelder has a silent-ish / soft feel in the gj- for English speakers; it is not pronounced like a hard English g in go
• -en at the end is the definite ending, usually pronounced lightly

For many learners, the most important thing is to recognize the sentence as:

• Registreringen | gjelder | adresseendringen og adressesperren

Breaking it into chunks makes it much easier to read.

Yes. Gjelder is the present tense form of å gjelde.

• å gjelde = to apply to / concern
• gjelder = applies to / concerns

So the sentence is in the present tense:

• Registreringen gjelder ... = The registration concerns / applies to ...

This is also the form you will most often see in notices, official texts, and rules.