Ég finn bækur sem eru mjög spennandi.

Finna is the infinitive form, finn is the 1st person singular present tense.

The verb is að finna (to find). In the present tense it conjugates as:

• ég finn – I find
• þú finnur – you (sg.) find
• hann / hún / það finnur – he / she / it finds
• við finnum – we find
• þið finnið – you (pl.) find
• þeir / þær / þau finna – they find

Because the subject is ég (I), you must use finn.

Finn is the normal active form: Ég finn bækur… – I find books…

Finnst is the middle/impersonal form and is often used for opinions or feelings, like I think / I feel / It seems to me:

• Mér finnst þessi bók góð. – I think this book is good. (literally: To me finds this book good.)

So:

• Ég finn bækur. – I (physically/actively) find books.
• Mér finnst þessi bók góð. – I think this book is good.

You would not use finnst with a direct object like bækur in this meaning.

Bækur is the plural of bók (a book).

The main forms are:

• Singular:

  • nominative: bók
  • accusative: bók
  • dative: bók
  • genitive: bókar

• Plural:

  • nominative: bækur
  • accusative: bækur
  • dative: bókum
  • genitive: bóka

In Ég finn bækur…, bækur is the object, so it is in the accusative plural. For this word, nominative and accusative plural look the same: bækur.

Icelandic usually attaches the definite article to the noun as a suffix instead of using a separate word.

• bækur – books
• bækurnar – the books

So if you wanted to say I find the books that are very exciting, you would say:

• Ég finn bækurnar sem eru mjög spennandi.

Sem introduces a relative clause, similar to that / which / who in English.

• bækur sem eru mjög spennandi
  → books that are very exciting

Structure:

• bækur – the noun being described
• sem – that/which
• eru mjög spennandi – the clause describing the books

You cannot just drop sem here; you need it to connect the clause to bækur.

Eru is the 3rd person plural form of vera (to be).

Present tense of vera:

• ég er – I am
• þú ert – you are
• hann / hún / það er – he/she/it is
• við erum – we are
• þið eruð – you (pl.) are
• þeir / þær / þau eru – they are

The subject of the relative clause is bækur (books), which is plural, so you must use the plural form eru:

• bækur sem eru mjög spennandi – books that are very exciting

Mjög means very. It’s an adverb that modifies adjectives and some other adverbs.

Here it modifies spennandi:

• mjög spennandi – very exciting

It normally comes directly before the adjective/adverb it modifies:

• mjög góður – very good
• mjög fljótt – very quickly

In the sentence, mjög spennandi together describes the books:

• bækur sem eru mjög spennandi – books that are very exciting

Spennandi is a present participle (from a verb related to spenna / spenna – tension/excitement) used like an adjective meaning exciting.

Important point: adjectives ending in -andi like spennandi, skemmtandi (entertaining), etc. are indeclinable in modern Icelandic. They keep the same form regardless of:

• gender (masc./fem./neut.)
• number (sing./pl.)
• case

So you get:

• spennandi bók – an exciting book
• spennandi bækur – exciting books
• um spennandi bækur – about exciting books

Spennandi stays the same in all of those.

Yes, Ég finn mjög spennandi bækur is correct and natural.

The nuance:

• Ég finn mjög spennandi bækur.
  → I find very exciting books. (adjective phrase in front of the noun)

• Ég finn bækur sem eru mjög spennandi.
  → I find books that are very exciting. (relative clause after the noun)

In most everyday contexts, they mean almost the same thing. The version with sem eru… can feel a bit more descriptive or explanatory, but both are fine.

You can, but the meaning shifts slightly.

• Ég finn bækur sem eru mjög spennandi.
  → I (generally) find books that are very exciting. (simple present, habitual or general fact)

• Ég er að finna bækur sem eru mjög spennandi.
  → I am (right now / these days) in the process of finding books that are very exciting.

Vera að + infinitive (here: er að finna) often corresponds to English am/is/are doing and emphasizes an ongoing process rather than a general statement.

Approximate pronunciation (using English-like hints):

• Ég – like yeh with a soft y and a bit of a glide, often close to [jɛː]
• finn – like English fin ([fɪn])
• bækur – bæ like bye but shorter, kur like kurr → roughly BYE-kur ([ˈpaiːkʏr])
• sem – like sem in semiconductor; short e ([sɛm])
• eru – e like bed, ru like reh-ru → EH-ru ([ˈɛːrʏ])
• mjög – roughly myerg with rounded lips; a bit like myugg ([mjœːɣ])
• spennandi – spen like spen in spend, nan like nun but with a, di like dih → SPEN-nahn-dih ([ˈspɛnːantɪ])

Icelandic vowels and consonants don’t always match English sounds exactly, but these approximations are close enough for a learner to be understood.