Geturðu hellt vatni í glösin á bakkanum?

Geturðu is a common contracted form of getur þú.

• getur = can, is able to (2nd person singular of geta)
• þú = you (singular, informal)

So Geturðu...? means Can you...?

This contraction is very normal in speech and writing:

• getur þú → geturðu
• vilt þú → viltu
• ætlar þú → ætlarðu

After geta (can), Icelandic usually uses the verb in the supine form rather than the dictionary infinitive.

So:

• dictionary form: hella = to pour
• after getur: hellt

That is why the sentence says:

• Geturðu hellt ... ? = Can you pour ... ?

This is very common with modal verbs in Icelandic:

• Ég get lesið. = I can read.
• Hún getur skrifað. = She can write.
• Geturðu hellt...? = Can you pour...?

For an English speaker, this feels unusual because English uses the plain infinitive/base form after can.

Because the verb hella takes the thing being poured in the dative.

So:

• vatn = water (basic form / nominative-accusative)
• vatni = water in the dative

In this sentence, vatni is the thing being poured, so it appears in dative:

• hellt vatni = poured water

This is something you often just have to learn with the verb:

• hella einhverju í eitthvað
  = pour something into something

So the pattern is:

• einhverju = dative
• eitthvað after í when there is motion into something

Because í can take different cases depending on meaning:

• accusative = movement into
• dative = location in

Here the water is being poured into the glasses, so Icelandic uses the accusative:

• í glösin = into the glasses

Compare:

• Vatnið er í glösunum. = The water is in the glasses.
  Here there is no movement, only location, so dative is used.

This motion-vs-location contrast is very important with Icelandic prepositions.

Because á also changes case depending on meaning:

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

In this sentence, the tray is just the location of the glasses:

• á bakkanum = on the tray

So bakkanum is the dative singular definite form of bakki (tray).

Compare:

• Ég set glösin á bakkann. = I put the glasses onto the tray.
  movement → accusative
• Glösin eru á bakkanum. = The glasses are on the tray.
  location → dative

Glösin means the glasses.

Breakdown:

• glas = glass
• glös = glasses (plural)
• glösin = the glasses (definite plural)

The vowel changes from a to ö in the plural:

• glas → glös

That kind of vowel change is common in Icelandic nouns.

The ending -in is the definite article attached to the noun:

• glös = glasses
• glösin = the glasses

So í glösin = into the glasses.

It can be either, just like English Can you...?

In many situations, Geturðu hellt vatni í glösin á bakkanum? is understood as a polite request:

• Can you pour water into the glasses on the tray?

It does not always mean the speaker is literally asking whether you have the physical ability.

If you want to sound a little softer or more tentative, Icelandic can also use forms like:

• Gætirðu ... ? = Could you ... ?

But Geturðu ... ? is very normal and natural.

Most naturally, it describes the glasses:

• glösin á bakkanum = the glasses on the tray

So the sentence is understood as:

• Can you pour water into the glasses that are on the tray?

In other words, á bakkanum is most likely attached to the noun phrase glösin rather than describing where the pouring happens.

English can have the same kind of structure:

• the glasses on the tray

Icelandic usually adds the definite article to the end of the noun instead of using a separate word.

So:

• glas = a glass / glass
• glasið = the glass
• glös = glasses
• glösin = the glasses
• bakki = tray
• bakkinn = the tray
• bakkanum = on the tray / to the tray, depending on case and context

This is why you do not see a separate word for the in the sentence. The definiteness is built into glösin and bakkanum.

It is addressing one person.

That is because:

• þú = you singular
• Geturðu = Can you? addressed to one person

If you were speaking to more than one person, you would use þið:

• Getið þið hellt vatni í glösin á bakkanum?
  = Can you all pour water into the glasses on the tray?

So Geturðu is singular.