Mit medlemskab er stadig gyldigt, så jeg kan bruge døren ved siden af receptionen.

Because medlemskab is a neuter noun in Danish, and neuter nouns take et in the indefinite form and mit in the possessive.

• et medlemskab = a membership
• mit medlemskab = my membership

Compare:

• en bil → min bil
• et medlemskab → mit medlemskab

So the form of my depends on the grammatical gender of the noun.

Medlemskab means membership.

It is a single Danish noun, built from:

• medlem = member
• -skab = a noun ending that can form an abstract state or condition

So medlemskab is the state of being a member: membership.

This is also a good example of how Danish often makes one-word compounds where English may also use one word, but sometimes learners still expect a phrase instead.

Because gyldig is an adjective, and here it describes the neuter noun medlemskab.

When an adjective is used with a neuter singular noun, it often gets -t:

• en gyldig billet = a valid ticket
• et gyldigt medlemskab = a valid membership

Even though the adjective comes after er, the agreement still shows:

• Mit medlemskab er gyldigt.

This is called predicative adjective agreement.

Stadig means still.

So:

• Mit medlemskab er stadig gyldigt = My membership is still valid

It shows that the membership continues to be valid now, probably despite some possible doubt or time having passed.

That is the normal word order in a main clause like this.

In Danish, the finite verb usually comes early in the clause, and adverbs like stadig often come after it:

• Mit medlemskab er stadig gyldigt

Compare with English:

• My membership is still valid

So the placement is very similar to English here.

Here så means so, therefore, or as a result.

It links the two ideas:

• My membership is still valid
• so I can use the door next to the reception

It is functioning as a coordinating connector between two main clauses.

Good question. Danish does often use inversion, but not after every linking word.

Here så is being used like a coordinating conjunction between two main clauses, so the second clause keeps normal main-clause order:

• så jeg kan bruge døren...

That means:

• jeg = subject
• kan = finite verb

No inversion is needed here.

You often see inversion after adverbs placed first in a clause, for example:

• Derfor kan jeg bruge døren. = Therefore I can use the door.

But in your sentence, så simply links the two clauses.

Kan means can / am able to, and bruge means use.

Together:

• jeg kan bruge døren = I can use the door

This is a normal modal verb construction in Danish:

• kan = finite modal verb
• bruge = infinitive

Like in English, after a modal verb you use the basic form of the main verb:

• jeg kan komme = I can come
• jeg kan bruge døren = I can use the door

Because it refers to a specific door, not just any door.

• en dør = a door
• døren = the door

In this sentence, the door is identified by the phrase:

• ved siden af receptionen = next to the reception

So it is a particular, known door:

• the door next to the reception

Ved siden af means next to or beside.

It is a fixed expression:

• ved = by / at
• siden = side
• af = of

But you should learn it as a whole phrase:

• ved siden af receptionen = next to the reception

This is much more natural than trying to translate each word separately every time.

Because Danish usually uses the definite form when talking about a specific, known place in a building.

• en reception = a reception / reception desk
• receptionen = the reception / the front desk

So:

• ved siden af receptionen = next to the reception

This sounds natural because both speaker and listener are assumed to know which reception is meant.

It can mean either, depending on context.

In many everyday situations, receptionen can refer to:

• the reception desk
• the reception area
• the staff at reception

In your sentence, døren ved siden af receptionen most naturally means the door next to the reception/front desk area.

Because the sentence contains two full clauses:

• Mit medlemskab er stadig gyldigt
• så jeg kan bruge døren ved siden af receptionen

The comma helps separate the two parts. In written Danish, punctuation often marks clause boundaries clearly.

So the comma here is completely natural.

Normally, no. The correct standard Danish word here is gyldigt from gyldig.

• gyldig / gyldigt = valid

The word valid exists in some contexts because of English influence, but it is not the normal everyday choice here. For standard Danish, use:

• Mit medlemskab er stadig gyldigt.

In neutral speech, the main stress would usually fall on the important content words, for example:

• Mit medlemskab er stadig gyldigt, så jeg kan bruge døren ved siden af receptionen.

If you want contrast or emphasis, you could stress different words:

• Mit medlemskab...
  if you are contrasting it with someone else’s
• er stadig gyldigt
  if the important point is that it is still valid
• bruge døren
  if the specific access point matters

So the stress depends on what information is most important in context.