Bókin er ofan á borðinu.

Because -in is the definite article attached to the noun.

• bók = book
• bókin = the book

Icelandic usually puts the at the end of the noun instead of using a separate word before it.

Also, bók is a feminine noun, and here bókin is in the nominative singular because it is the subject of the sentence.

Er means is.

It is the 3rd person singular present tense of the verb vera, which means to be.

So:

• ég er = I am
• þú ert = you are
• hann / hún / það er = he / she / it is

In this sentence, Bókin er ... means The book is ...

Ofan á means on top of or up on.

It is used when something is resting on the top surface of something else.

So Bókin er ofan á borðinu means the book is on top of the table, not under it, inside it, or just somewhere near it.

Learners often compare it with á, which can also mean on. In many situations, á borðinu is enough for on the table. But ofan á can sound a bit more explicit, emphasizing that something is on top of a surface.

Borðinu is the noun borð with both:

• the definite article: the table
• the dative singular ending

So:

• borð = table
• borðið = the table
• borðinu = the table in the dative

Here that happens because á takes the dative when it describes location.

So in this sentence:

• ofan á borðinu = on top of the table

Because Icelandic often changes case depending on whether you mean:

• location: where something is
• movement toward a place: where something goes

With á:

• dative = location
• accusative = movement onto something

Compare:

• Bókin er á borðinu. = The book is on the table.
  
  • location → dative
• Ég set bókina á borðið. = I put the book onto the table.
  
  • movement → accusative

In your sentence, the book is already there, so Icelandic uses dative: borðinu.

Bókin is in the nominative case.

That is because it is the subject of the sentence: it is the thing that is somewhere.

So the basic structure is:

• Bókin = subject, nominative
• er = verb
• ofan á borðinu = location phrase

This is very typical Icelandic sentence structure.

Yes. That is a very common sentence and often the most natural way to say The book is on the table.

The difference is mainly nuance:

• á borðinu = on the table
• ofan á borðinu = on top of the table, a bit more explicit

So if you simply want to say where the book is, á borðinu is often enough. If you want to stress that it is specifically on top of the table, ofan á borðinu works well.

It is written as two words: ofan á.

Even though it is two words, learners should often treat it as a set expression meaning on top of.

You will see many Icelandic location expressions like this, where a short combination functions almost like a single prepositional unit.

Yes. This is a very normal, straightforward order:

• Bókin = subject
• er = verb
• ofan á borðinu = place expression

So it follows the basic pattern:

subject + verb + location

Icelandic word order can change for emphasis, especially in longer sentences, but this version is the most neutral and beginner-friendly one.

Because Icelandic usually expresses the by attaching it to the end of the noun.

So instead of separate words like English:

• the book
• the table

Icelandic commonly uses:

• bókin
• borðið / borðinu

This is one of the first big differences English speakers notice. The noun ending carries a lot of information at once:

• the noun itself
• whether it is definite
• its case
• its number
• sometimes clues about gender

A rough English-friendly guide would be:

Bókin er ofan á borðinu
≈ BOH-kin er OH-van ow BOR-thi-nu

A few helpful notes:

• ó is a long vowel, roughly like o in go
• ð is like the th in this, though pronunciation can vary a bit depending on position
• á is like ow in cow
• the stress in Icelandic usually falls on the first syllable of each word

So the main stresses are:

• BÓ-kin
• OF-an
• BOR-ði-nu