Fríið byrjar á morgun.

Because Icelandic usually puts the definite article on the end of the noun instead of using a separate word like English the.

• frí = holiday, vacation, break, time off
• fríið = the holiday / the vacation / the break

So -ið here is the neuter singular definite ending. A learner can think of fríið as frí + the.

Frí is a very common Icelandic word for time off. Depending on context, it can mean:

• a vacation
• a holiday
• a break
• time off from work or school

So in Fríið byrjar á morgun, the exact English translation could vary a little depending on context, but the grammar stays the same.

Byrja is the infinitive, meaning to begin or to start.
In the sentence, the verb has to match the subject and be in a finite form:

• byrja = to begin
• byrjar = begins / starts

Here the subject is fríið (the vacation / the break), which is third person singular, so Icelandic uses byrjar.

Á morgun means tomorrow.

Even though English uses a single word, Icelandic uses this fixed expression:

• á morgun = tomorrow

For learners, it is best to memorize it as a whole phrase rather than trying to translate each part literally.

A very important contrast is:

• á morgun = tomorrow
• í morgun = this morning

Those are easy to confuse, so they are worth learning together.

Because standard Icelandic normally uses the full expression á morgun.
Here morgun is part of a set time expression, not just a plain standalone noun meaning morning.

So if you want to say tomorrow, use á morgun, not just morgun.

This sentence uses a very normal Icelandic word order:

• Fríið = subject
• byrjar = verb
• á morgun = time expression

So:

• Fríið byrjar á morgun. = The vacation starts tomorrow.

But Icelandic can also move the time expression to the front:

• Á morgun byrjar fríið.

That is also correct. When Icelandic puts something else first, the verb still normally stays in second position. This is a very important Icelandic pattern.

A rough English-friendly guide is FREE-ith, though that is only approximate.

A few helpful points:

• í sounds like ee in see
• the written ð is a soft sound, somewhat like th in this
• because fríið has íi, there is a slight separation between the vowels rather than one simple English-style syllable

So it is not pronounced exactly like an English word, but FREE-ith is a useful first approximation.

A rough approximation is:

FREE-ith BIR-yar au MOR-gun

More specifically:

• Fríið ≈ FREE-ith
• byrjar ≈ BIR-yar
• á ≈ ow in cow
• morgun ≈ MOR-gun

This is only approximate, but it is a good starting point for an English speaker.

Yes. In many contexts, byrja can be translated as either start or begin.

So all of these are natural translations of the sentence, depending on style:

• The vacation starts tomorrow.
• The vacation begins tomorrow.
• The break starts tomorrow.

English choice depends on context and tone more than on a grammatical difference in Icelandic.

Yes. A common alternative is hefst, from hefjast, which also means begins:

• Fríið hefst á morgun.

That sounds a bit more formal or written in some contexts.
Fríið byrjar á morgun is very natural and everyday.

Because Icelandic often begins with the topic or subject if nothing special is being emphasized. Here the sentence is simply presenting the information in a neutral way:

• Fríið byrjar á morgun. = neutral statement

If you want to emphasize tomorrow, you might put that first:

• Á morgun byrjar fríið.

So the original version is just the straightforward, unmarked order.