Handtaskan mín er þung í dag, af því að ég er með bók og tölvu.

In Icelandic, possessives like mín often come after the noun, especially when the noun is definite.

• handtaska = handbag
• handtaskan = the handbag
• handtaskan mín = my handbag

So -an is the definite article attached to the noun, and mín comes after it.

You can sometimes see possessives before the noun in other contexts, but noun + definite article + possessive is a very common and natural pattern.

The ending -an is the definite article, meaning the.

So:

• handtaska = handbag
• handtaskan = the handbag

Unlike English, Icelandic usually attaches the to the end of the noun instead of writing it as a separate word.

Because the sentence says handtaskan mín, it literally looks something like the handbag my, but in natural English that is just my handbag.

The possessive my changes form to match the noun’s gender, number, and case.

Here, handtaska is:

• feminine
• singular
• in the nominative case

So the correct form is mín.

Compare:

• minn for some masculine nouns
• mín for feminine nouns
• mitt for neuter nouns

So handtaskan mín is feminine singular nominative, which is why mín is used.

Adjectives in Icelandic must agree with the noun they describe.

Here, the noun being described is handtaskan, which is:

• feminine
• singular
• nominative

So the adjective takes the feminine singular nominative form:

• þungur = masculine
• þung = feminine
• þungt = neuter

That is why the sentence says Handtaskan mín er þung.

Í dag means today.

This is a fixed and very common Icelandic expression:

• í = in
• dag = day (in this expression)

So literally it is something like in day, but idiomatically it means today.

You should learn í dag as a set phrase.

Af því að means because.

It introduces a reason:

• Handtaskan mín er þung í dag = My handbag is heavy today
• af því að... = because...
• ég er með bók og tölvu = I have a book and a computer / I’m carrying a book and a computer

So the second part explains why the bag is heavy.

This is a very common way to say because in everyday Icelandic.

Yes, literally ég er með means I am with, but in Icelandic it is very often used to mean:

• I have
• I’m carrying
• I’ve got

So in this sentence, ég er með bók og tölvu means something like:

• I have a book and a computer with me
• I’m carrying a book and a computer

This is a very common everyday structure in Icelandic, especially in speech.

Icelandic does have ways to express possession, but vera með (to be with) is extremely common in spoken language when talking about having something on you, with you, or available.

So:

• ég er með bók og tölvu feels natural for I have/am carrying a book and a computer
• it can suggest that these items are with the speaker right now

In this sentence, that fits perfectly: the bag is heavy because the speaker has those things in it or with them.

They are in the accusative singular, because the expression vera með normally takes the object in the accusative.

So:

• dictionary form: bók = book
• dictionary form: tölva = computer

In this sentence:

• bók stays bók
• tölva becomes tölvu

This happens because nouns change form depending on case.

So með bók og tölvu shows normal Icelandic case marking after vera með.

Different nouns decline differently.

Here:

• bók has the same form in nominative and accusative singular
• tölva changes in the accusative singular to tölvu

So even though both nouns are in the same case, they do not necessarily look the same. That is very normal in Icelandic.

This is something learners gradually get used to: case is important, but the visible change depends on the noun’s declension pattern.

In standard written Icelandic, a comma before a subordinate clause like af því að is normal.

So:

• Handtaskan mín er þung í dag, af því að...

That comma helps separate the main clause from the explanation clause.

In speech, of course, you just hear a pause or a natural flow rather than seeing punctuation.

Yes. In less formal language, especially in speech, people may say því að instead of af því að.

Both can mean because, though af því að is very clear and common.

So a learner should definitely recognize both:

• af því að = because
• því að = because

In your sentence, af því að is completely natural.

The structure is:

• Handtaskan mín = subject
• er = is
• þung = complement/adjective
• í dag = time expression
• af því að... = reason clause

So the sentence is built like this:

My handbag + is + heavy + today + because...

Then the reason clause:

• ég = I
• er með = have/am carrying
• bók og tölvu = a book and a computer

This is a very typical and useful Icelandic sentence pattern: statement first, explanation after.