Hún segir mér hvaða flipa ég á að smella á í vafranum.

Because segja normally takes the person you tell in the dative case:

• segja mér = tell me
• segja honum = tell him
• segja henni = tell her

So in Hún segir mér ..., mér is the dative form of ég.

A useful pattern is:

• segja einhverjum eitthvað = to tell someone something

Here, mér is someone.

Hvaða means which or what kind of, depending on context. In this sentence it introduces an indirect question:

• hvaða flipa ... = which tab ...

Compare:

• Hvaða flipa á ég að smella á? = direct question
• Hún segir mér hvaða flipa ég á að smella á. = indirect question

So it works a lot like English which in She tells me which tab I should click on.

Because flipa is the accusative singular form of flipi.

The noun is:

• nominative: flipi
• accusative: flipa

It appears in the accusative here because smella á takes an object with á, and in this usage that gives you á + accusative:

• smella á flipa = click on a tab

So hvaða flipa means which tab.

They are doing two completely different jobs.

1. The first á is the verb eiga in the present tense:

   • ég á = I own / I am supposed to / I have to, depending on context

2. The second á belongs to the expression smella á:

   • smella á = click on

So:

• ég á að smella á = I am supposed to click on

It looks repetitive, but grammatically it is perfectly normal.

Historically it comes from eiga meaning own, but in modern Icelandic eiga að + infinitive is a very common expression meaning:

• be supposed to
• should
• sometimes have to

So here ég á að smella á does not mean ownership. It means something like:

• I should click on
• I am supposed to click on

This is one of the most common Icelandic ways to express obligation or instruction.

Here að is the infinitive marker, like English to in to click.

So:

• smella = click
• að smella = to click

After eiga að, you normally get this pattern:

• ég á að fara = I should go
• þú átt að lesa = you should read
• ég á að smella á = I should click on

So að is not a preposition here; it is marking the infinitive.

Because this is an indirect question, not a direct question.

In a direct question, Icelandic usually has verb-second / question order:

• Hvaða flipa á ég að smella á?
• Which tab should I click on?

But after a verb like segir, it becomes an embedded clause, and the order is more like a statement:

• Hún segir mér hvaða flipa ég á að smella á.

So the subject ég comes before á.

This is very similar to English:

• direct: Which tab should I click on?
• indirect: She tells me which tab I should click on.

Because í means in, and when it shows location it usually takes the dative case.

Here the meaning is in the browser as a location, not motion into it. So you get:

• í vafranum = in the browser

Compare the general rule:

• í + dative = in, inside, at rest
• í + accusative = into, motion toward the inside of something

So:

• í vafranum = in the browser
• í vafrann would suggest motion into the browser, which is not the idea here

It is the noun vafri with both:

• the dative singular ending, and
• the definite article attached

The base noun is:

• vafri = browser

In Icelandic, the definite article is usually attached to the end of the noun instead of being a separate word like English the.

So:

• vafri = a browser
• vafrinn = the browser
• í vafranum = in the browser

The exact form changes with case, number, and gender, so -num here reflects dative singular definite.

Yes. In computer-related Icelandic, smella á is a very common way to say click on.

Examples:

• smella á hnappinn = click the button / click on the button
• smella á hlekkinn = click the link
• smella á flipa = click on a tab

So it is best to learn smella á as a unit, not just smella by itself.

In modern Icelandic, hvaða is generally treated as indeclinable in this use, so it stays hvaða regardless of the noun after it.

That means you get:

• hvaða flipa
• hvaða bók
• hvaða hús

The noun itself shows the case more clearly than hvaða does. In this sentence, the important case marking is really on flipa, not on hvaða.