Gasgrillið er á veröndinni.

A simple breakdown is:

• Gasgrillið = the gas grill
• er = is
• á veröndinni = on the veranda / on the patio

So the structure is:

• subject: Gasgrillið
• verb: er
• location phrase: á veröndinni

Because Icelandic very often makes compound nouns.

Here, gas + grill become gasgrill = gas grill.
Then the definite article is added to the end:

• gasgrill = a gas grill
• gasgrillið = the gas grill

So Icelandic does in one word what English usually does in two or three.

The ending -ið is the definite article attached to the noun, so it means the.

In this sentence:

• gasgrill = gas grill
• gasgrillið = the gas grill

More specifically, -ið is the definite ending you commonly see with a neuter singular noun in the nominative here.

In Icelandic, the is usually not a separate word. Instead, it is attached to the end of the noun.

For example:

• verönd = veranda / patio

• veröndin = the veranda / the patio

• gasgrill = gas grill
• gasgrillið = the gas grill

So this sentence has no separate word for the because Icelandic normally expresses definiteness with a suffix.

Because the noun is not standing alone as the subject. It comes after the preposition á, and here that preposition requires a different case.

The base forms are roughly:

• verönd = veranda / patio
• veröndin = the veranda (nominative)
• veröndinni = the veranda (dative)

So veröndinni is used because the phrase á veröndinni is a location phrase.

Veröndinni is dative singular definite.

The reason is that á can take different cases depending on meaning:

• dative for location: being on / at something
• accusative for motion toward / onto something

Here the grill is already located there, so Icelandic uses dative:

• Gasgrillið er á veröndinni = the gas grill is on the veranda

Compare that with motion:

• Ég fer á veröndina = I go out onto the veranda

That contrast is very common in Icelandic.

Here á means on in the sense of located on / out on / at the veranda or patio.

Prepositions do not match English perfectly word for word, so it is best to learn á veröndinni as the normal Icelandic way to express this location.

A useful rule of thumb is:

• á + dative = location
• á + accusative = movement onto

A few useful pronunciation points:

• á is roughly like ow in now
• ö has no exact English equivalent, but it is somewhat like the vowel in burn, with rounded lips
• ð in -ið is like th in this
• Icelandic stress normally falls on the first syllable

So a rough learner-friendly approximation would be:

• gasgrillið ≈ GAS-grill-ith
• veröndinni ≈ VE-rund-in-ni with a rounded vowel in ö

That is only an approximation, but it helps as a starting point.

The given order is the most neutral one:

• Gasgrillið er á veröndinni.

But Icelandic word order is somewhat flexible. For emphasis, you could also put the location first:

• Á veröndinni er gasgrillið.

That sounds more like On the veranda is the gas grill or It is on the veranda that the gas grill is.

The neutral everyday order, though, is the one you were given.

It can overlap with several English words depending on context, such as:

• veranda
• patio
• porch
• sometimes something close to deck

So the exact English translation depends on the situation. In a learning sentence like this, the most important thing is to recognize veröndinni as a place expression meaning something like on the veranda / patio.