Learn Hardcore Icelandic: Gesturinn kemur með blóm fyrir mömmu.

gesturinn comes from the noun gestur (“guest”) plus the definite suffix -inn, so it literally means “the guest.” In Icelandic there is no separate word for “the”; instead you attach -inn (or another ending) to the noun.

What case and number is gesturinn in?

It’s nominative singular definite.

Nominative because it’s the subject of the sentence.
Singular because it refers to one guest.
Definite because of the suffix -inn.

What does kemur með mean?

kemur is the 3rd person singular present of koma (“to come”), and með means “with.” Combined, kemur með means “comes with,” which in English we translate as “brings” (i.e. “He brings flowers”).

Why is the verb koma used here instead of bera (“to carry”) or flytja (“to transport”)?

In Icelandic the usual way to say “to bring something to someone” is koma með. While bera can mean “to carry” and flytja “to move/transport,” when you are “bringing” an item as a gift or to someone’s place, you almost always use koma með.

What does blóm mean? Is it singular or plural?

blóm means “flower” or “flowers.” It’s a neuter noun whose nominative and accusative forms are identical in both singular and plural. Here context (“brings flowers”) tells us it’s plural.

What case is blóm in, and why?

It’s in the accusative case because it’s the direct object of the verb phrase koma með.

What does fyrir mean in this sentence, and which case does it govern?

fyrir means “for” in the sense of “intended for someone.” It governs the accusative case, so the noun following fyrir must be accusative.

Why is it mömmu and not mamma or móðir?

mamma is the basic (nominative) form “mom.” After fyrir, which takes accusative, the weak feminine noun mamma changes to mömmu.
móðir is a more formal word for “mother” and would decline differently (e.g. accusative móður).

How would you say “for my mom” or “for her mom” in Icelandic?

You add a matching possessive pronoun in the same case (accusative after fyrir):

“for my mom” = fyrir mömmu mína
“for her mom” = fyrir mömmu hennar
“for his mom” = fyrir mömmu hans