Learn Hardcore Icelandic: Hann keyrir rólega.

Both. Icelandic simple present often covers habitual and right-now actions, so it can mean either “He drives slowly” or “He is driving slowly,” depending on context. If you want to make the ongoing action explicit, you can say Hann er að keyra rólega (“He is driving slowly right now”). Note: vera að can also mean “about to” in some contexts, but with activity verbs like keyra it usually means “is doing (now).”

Why is it rólega and not rólegur?

Because rólega is an adverb modifying how he drives. Rólegur is an adjective and would describe the subject, not the manner of driving.

Hann er rólegur. = “He is calm.”
Hann keyrir rólega. = “He drives calmly/slowly.”

What’s the difference between rólega and hægt for “slowly”?

rólega literally means “calmly, gently,” and in everyday speech it also covers “slowly.” It hints at a relaxed, unhurried manner.
hægt (from hægur, “slow”) zeroes in on speed.
Examples:
Hann keyrir rólega. = He drives calmly/slowly (relaxed manner).
Hann keyrir hægt. = He drives slowly (low speed). You’ll also hear the set phrase hægt og rólega = “slowly and steadily.”
Note: hægt can also mean “possible” in other contexts (Það er hægt = “It’s possible”). Context disambiguates it.

Where does the adverb go, and how do I negate this?

Default neutral order is Subject–Verb–(Object)–Adverb:

Hann keyrir rólega.
Negation ekki follows the finite verb:
Hann keyrir ekki rólega. = “He doesn’t drive slowly.”

Can I start with the adverb for emphasis?

Yes. Icelandic main clauses are verb-second (V2), so if you front the adverb, the finite verb must still be second:

Rólega keyrir hann. (emphatic/poetic, “Slowly he drives.”)
Avoid: Hann rólega keyrir (ungrammatical in normal main-clause word order).

How does keyra conjugate?

Key forms:

Present: ég keyri, þú keyrir, hann/hún/það keyrir; við keyrum, þið keyrið, þau/þeir/þær keyra
Past: ég/hann keyrði, þú keyrðir; plural keyrðum, keyrðuð, keyrðu
Supine/Past participle: keyrt (e.g., Ég hef keyrt = “I have driven”)
Imperative: Keyrðu! (sg), Keyrið! (pl)
Present participle: keyrandi

Is there another verb for “to drive”?

Yes, aka is another verb: Hann ekur rólega. It’s common in formal/official contexts (e.g., laws, road signs), while keyra is more everyday speech. Both are correct.

What case is hann, and what are its other forms?

Hann is nominative (subject case). Other forms:

Accusative: hann
Dative: honum
Genitive: hans

How do I say it with other subjects (she/they/I/we)?

Hún keyrir rólega. (she)
Þeir keyra rólega. (they, masculine)
Þær keyra rólega. (they, feminine)
Þau keyra rólega. (they, neuter/mixed)
Ég keyri rólega. (I)
Við keyrum rólega. (we)
Þið keyrið rólega. (you, plural)

Can I drop the subject pronoun like in Spanish?

Generally no. Icelandic is not a pro-drop language; you normally include the subject pronoun: Hann keyrir rólega, not just Keyrir rólega (except in imperatives or very special contexts).

How do I make questions with this sentence?

Yes–no question (verb first): Keyrir hann rólega? = “Does he drive slowly / Is he driving slowly?”
Wh-question: Hvernig keyrir hann? = “How does he drive?” → Hann keyrir rólega.

How do I say “more slowly” or “most slowly”?

With rólega (manner): rólegar (more calmly/slowly), rólegast (most calmly/slowly)
- Hann keyrir rólegar en ég.
With hægt (speed): hægara (more slowly), hægast (most slowly)
- Hann keyrir hægara en ég.
  Both sets are fine; pick hægara/hægast when you want to be specifically about speed.

Can I intensify rólega?

Yes:

mjög rólega = very slowly/calmly
frekar rólega = rather/pretty slowly
ansi rólega = quite/pretty slowly
Avoid meira rólega for “more slowly”; use the comparative rólegar (or hægara).

Is rólega ever used by itself?

Yes, as an interjection: Rólega! = “Easy!” / “Take it easy!” / “Calm down!”

Any pronunciation tips for the whole sentence?

Hann: long n sound (nn). Approx: “han” with a lengthened n.
keyrir: initial k before ey is the soft “kj” sound; ey ≈ “ay”; roll/tap the r. Approx: “KAY-rir” with a light “ky” onset.
rólega: ó is a long “oh”; g between vowels is a soft voiced fricative (like a gentle “gh”). Approx: “ROH-le-gha.”
Stress is always on the first syllable of each word.

Is anything “missing,” like an article?

No. Pronouns don’t take articles, and Icelandic doesn’t use a separate word for “the.” Definiteness is shown with a suffix on nouns (not relevant here).

Why is it keyrir and not keyrar?

Many verbs with infinitive ending in -a take -ir in 2nd/3rd person singular present: þú keyrir, hann keyrir. Also note spelling: y and i are pronounced the same in modern Icelandic; keyrir uses y by spelling convention.