Om du vill ha ett medlemskap, finns det ett bra erbjudande den här veckan.

Om means if here. It introduces a condition:

• Om du vill ha ett medlemskap = If you want a membership

So this first part is a conditional clause, explaining when the second part is relevant.

In Swedish, vilja often works with another verb in the infinitive, just like want to in English.

• vill ha = want to have / want to get

So:

• du vill ha ett medlemskap = you want a membership

Swedish uses ha here where English might simply say want. This is very common.

After modal-like verbs such as vill, Swedish normally does not use att before the infinitive.

For example:

• Jag vill ha kaffe. = I want coffee.
• Hon kan simma. = She can swim.
• Vi måste gå. = We must go.

So vill ha is correct, not vill att ha.

Because medlemskap is an ett-word in Swedish.

That means its indefinite form takes ett:

• ett medlemskap = a membership

This is something you usually have to learn with the noun:

• en bok
• ett hus
• ett medlemskap

A useful pattern is that many nouns ending in -skap are ett-words, though you should still learn each noun individually.

Here, finns det means there is.

The basic pattern is:

• det finns = there is / there are

So:

• det finns ett bra erbjudande = there is a good offer

The det here does not mean a specific it. It works more like English there in there is.

This is because of Swedish word order.

The sentence begins with a clause:

• Om du vill ha ett medlemskap

After something is placed first in a Swedish main clause, the finite verb usually comes next. This is the V2 rule.

So the main clause becomes:

• finns det ett bra erbjudande

rather than:

• det finns ett bra erbjudande

Compare:

• Det finns ett bra erbjudande den här veckan.
• Om du vill ha ett medlemskap, finns det ett bra erbjudande den här veckan.

In the second sentence, the om-clause takes the first position, so finns comes before det.

The comma is acceptable, especially because the sentence starts with a longer introductory clause.

• Om du vill ha ett medlemskap, finns det ett bra erbjudande den här veckan.

In modern Swedish, commas after introductory clauses are often optional, especially in shorter sentences. So you may also see:

• Om du vill ha ett medlemskap finns det ett bra erbjudande den här veckan.

Both are understandable. The comma mainly helps readability here.

Because bra is an irregular adjective that does not change form.

Normally, many adjectives add -tt with ett-words:

• ett stort hus
• ett fint erbjudande

But bra stays bra:

• en bra bok
• ett bra erbjudande
• bra böcker

So ett bra erbjudande is correct.

Erbjudande usually means offer, deal, or special offer, depending on context.

So in this sentence:

• ett bra erbjudande = a good offer / a good deal

It is often used in shopping, advertising, and membership situations.

Den här veckan means this week.

It is made up of:

• den här = this
• veckan = the week

This may look strange at first, because Swedish often uses a kind of double definiteness with expressions like this.

So:

• den här veckan = this week
• den här boken = this book

This is a very common everyday pattern.

Because with den här / det här / de här, Swedish normally uses the noun in its definite form too.

So you get:

• den här veckan
• den här bilen
• det här huset

This is normal Swedish grammar. Even though English just says this week, Swedish uses a structure that literally looks more like this the-week.

Both mean this week, but they differ in style.

• den här veckan = very common in everyday speech
• denna vecka = more formal or written

So in ordinary spoken Swedish, den här veckan is often the more natural choice.

Swedish often uses time expressions without a preposition when English might also say them directly.

For example:

• den här veckan = this week
• idag = today
• förra året = last year

So you do not need a preposition like på here.

Yes, it is natural and correct.

• ha ett medlemskap means have a membership
• in some contexts it can also mean want to get a membership

Depending on the situation, Swedish might also use:

• bli medlem = become a member

But in this sentence, vill ha ett medlemskap works well if the idea is about wanting a membership product or plan.

Yes. Just like English there is / there are, Swedish det finns can be used for both singular and plural situations.

Examples:

• Det finns ett erbjudande. = There is an offer.
• Det finns flera erbjudanden. = There are several offers.

In your sentence, it is singular because of ett bra erbjudande.