Hjálmurinn gerir göngutúrinn í snjónum öruggari.

The ending -inn is the definite article (like English the) attached to the end of masculine nouns in Icelandic.

• hjálmur = helmet → hjálmurinn = the helmet
• göngutúr = walk (a walk, a stroll) → göngutúrinn = the walk / the stroll

In Icelandic, the definite article is usually a suffix on the noun, not a separate word as in English.

• hjálmurinn is the subject of the sentence (the thing doing the action). It is in the nominative singular definite: the helmet.
• göngutúrinn is the direct object, the thing being affected by the action of the verb gera (to make). It is in the accusative singular definite: the walk.

For this particular noun, the nominative and accusative forms with -inn are spelled the same (göngutúrinn), so you know it is the object from the verb pattern: gera + [object] + [adjective].

The verb gera usually means to do or to make. In this sentence it has the causative meaning to make [something] [adjective]:

• gera eitthvað öruggara = to make something safer

So the pattern is:

• [subject] gerir [object] [adjective/comparative]
• Hjálmurinn gerir göngutúrinn öruggari.
  → The helmet makes the walk safer.

The prepositional phrase í snjónum (in the snow) just adds context to göngutúrinn (the walk).

öruggur is the base adjective: safe.
öruggari is the comparative form: safer / more safe.

Icelandic forms comparatives by adding -ari to the adjective stem:

• öruggur → öruggari (safe → safer)
• stór → stærri (big → bigger)

We use the comparative here because the sentence describes a change in degree of safety: the helmet makes the walk more safe than without the helmet.

No, that would not be natural Icelandic.

English often uses more + adjective (e.g. more safe), but Icelandic normally uses a single comparative form:

• öruggari, not meira öruggur
• áhugaverðari, not meira áhugaverður (more interesting)

meira (more) is used mostly with verbs and nouns (e.g. gera meira – do more, meira vatn – more water), not to build the standard comparative of adjectives.

snjónum is dative singular definite of snjór (snow).

• Base form: snjór = snow
• Dative singular indefinite: snjó = (some) snow
• Dative singular definite: snjónum = the snow

The preposition í (in, into) can take either dative or accusative:

• í
  • dative → location, in/inside
    
    • í snjónum = in the snow (somewhere in snow)
• í
  • accusative → movement into / to something

Here we are describing where the walk takes place (location), so í needs the dative, and the speaker chooses the definite form: í snjónum = in the snow.

Grammatically and naturally, í snjónum modifies göngutúrinn, not hjálmurinn.

The structure is:

• Hjálmurinn (subject)
• gerir (verb)
• göngutúrinn í snjónum (object + its modifier)
• öruggari (resulting state / complement)

So it means: The helmet makes *the walk in the snow safer.
It does *not mean that the helmet is in the snow; it is the walk that is taking place in the snow.

You can move í snjónum, and both orders are possible:

• Hjálmurinn gerir göngutúrinn í snjónum öruggari.
• Hjálmurinn gerir göngutúrinn öruggari í snjónum.

The first version (from your sentence) slightly emphasizes the walk in the snow as a unit. The second puts a bit more emphasis on being safer in snow (as opposed to elsewhere).

Both are grammatically correct; Icelandic word order allows this kind of movement of adverbial phrases.

göngutúr is a compound noun:

• ganga = to walk (verb), also a noun a walk
• túr = trip, outing

Together göngutúr literally means walk‑trip and is the ordinary word for a walk / a stroll as an activity or outing.

So göngutúrinn is the walk (the outing, the stroll), not just the physical act of moving your legs.

• hj in hjálmurinn is pronounced like an unvoiced “hy” sound, a bit like the “h” in huge when some English speakers say hyuge. It is not like an English “sh” or “ch”.
• á in hjálmurinn is a long “ow” sound like in English cow.
• ö in öruggari is a rounded vowel, similar to the vowel in British English bird or German ö in schön.

Approximate pronunciations:

• hjálmurinn ≈ HYOWL-mur-in
• öruggari ≈ UR-ug-ga-ri (with the first syllable like English her but with rounded lips)