Litabókin er á borðinu við hliðina á kubbunum.

Because Icelandic very often makes compound nouns where English would use two words.

• lita = color / coloring
• bók = book
• litabók = coloring book

Then the definite article is added to the end:

• litabók = a coloring book
• litabókin = the coloring book

So Litabókin means the coloring book.

In Icelandic, the definite article is usually attached to the noun as an ending, not written as a separate word like English the.

In this sentence:

• litabókin = the coloring book
• borðinu = on the table
• kubbunum = beside the blocks

This is a very common feature of Icelandic.

Because the preposition á changes case depending on meaning.

With á:

• dative is usually used for location: on, in, at somewhere
• accusative is often used for motion toward something

Here the sentence describes where the coloring book is, not where it is moving. So Icelandic uses the dative:

• á borðinu = on the table

Compare:

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

So borðinu is the dative singular definite form of borð.

Because it is also in the dative plural definite.

The noun is:

• kubbur = block

Useful forms:

• kubbar = blocks
• kubbarnir = the blocks
• kubbunum = to/in/at/by the blocks, depending on the preposition

In this sentence, kubbunum comes after á in the fixed phrase við hliðina á. That á takes the dative, so we get:

• við hliðina á kubbunum = beside the blocks

They do two different jobs.

1. á borðinu

   • here á means on

2. við hliðina á kubbunum

   • here the second á is part of the expression við hliðina á, which means beside / next to

So even though both are spelled á, they belong to different parts of the sentence.

It is a very common Icelandic expression meaning:

• beside
• next to
• at the side of

Literally, it is built from:

• við = by / at / against
• hliðina = the side
• á = of/to/at here as part of the expression

You should usually learn við hliðina á as a whole chunk meaning next to.

Examples:

• við hliðina á húsinu = next to the house
• við hliðina á mér = next to me

Because in the expression við hliðina á, the word hliðina is in the accusative definite singular.

The noun is:

• hlið = side

Forms include:

• hlið = side
• hliðið = the side
• hliðina = the side (accusative definite)
• hliðinni = the side (dative definite)

In this fixed expression, Icelandic uses:

• við + accusative → við hliðina
• then á + dative → á kubbunum

So the whole phrase mixes two case patterns:

• við hliðina
• á kubbunum

That is one reason it is best memorized as a set phrase.

Yes. er is the present singular form of the verb vera = to be.

So:

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

In this sentence:

• Litabókin er ... = The coloring book is ...

It is capitalized only because it is the first word of the sentence.

In Icelandic, ordinary nouns are not capitalized the way they are in German. So in the middle of a sentence you would write:

• Ég sé litabókina. = I see the coloring book.

Not:

• Ég sé Litabókina.

The basic order here is:

• Litabókin = subject
• er = verb
• á borðinu við hliðina á kubbunum = location phrase

So it follows a straightforward pattern:

• Subject + verb + place

That is a very natural word order for a simple statement in Icelandic.

A more marked version is also possible, for example:

• Á borðinu við hliðina á kubbunum er litabókin.

But the original sentence is the most neutral and learner-friendly order.

In practice, it gives the location of the coloring book, but it often feels closely connected to borðinu:

• á borðinu við hliðina á kubbunum

This is naturally understood as:

• on the table beside the blocks or
• on the table, next to the blocks

So the whole phrase tells you where the coloring book is. English can show the same slight overlap:

• The coloring book is on the table next to the blocks.

Then Icelandic would usually switch from dative to accusative after á.

Current sentence:

• Litabókin er á borðinu. = The coloring book is on the table.
  
  • location → dative

With movement:

• Ég set litabókina á borðið. = I put the coloring book onto the table.
  
  • movement toward → accusative

So this sentence is a good example of an important Icelandic pattern: location vs. motion often changes the case after a preposition.

They are:

• litabók = coloring book
• borð = table
• kubbur = block
• hlið = side

The sentence uses inflected forms of these dictionary forms:

• litabókin ← litabók
• borðinu ← borð
• hliðina ← hlið
• kubbunum ← kubbur

This is very typical in Icelandic: the form you see in a sentence is often not the same as the dictionary form because of case, number, and definiteness.