Όταν η ομίχλη είναι πυκνή, οδηγώ πιο αργά.

In Greek, the verb ending usually already tells you who the subject is.

• οδηγώ = I drive
• οδηγείς = you drive
• οδηγεί = he/she/it drives

So Greek often leaves out the subject pronoun εγώ (I) unless it is needed for emphasis or contrast.

• Οδηγώ πιο αργά. = I drive more slowly.
• Εγώ οδηγώ πιο αργά. = I drive more slowly.
  This sounds more emphatic, like contrasting with someone else.

Όταν means when, but with the present tense it often has the sense of whenever or when(ever) in general statements.

So:

• Όταν η ομίχλη είναι πυκνή, οδηγώ πιο αργά.

can be understood as:

• When/Whenever the fog is thick, I drive more slowly.

This is very common in Greek for habitual situations.

Because the sentence describes a general, repeated situation, Greek uses the present tense in both parts:

• Όταν η ομίχλη είναι πυκνή = When the fog is thick
• οδηγώ πιο αργά = I drive more slowly

This is normal Greek usage for habits or general truths. English may also do this:

• When the fog is thick, I drive more slowly.

So there is no need for a future or special tense here.

Ομίχλη means fog, and it is a feminine noun in Greek. Because it is feminine singular, it takes the feminine singular definite article η.

• η ομίχλη = the fog

Greek nouns have grammatical gender, and you usually need to learn each noun together with its article:

• η ομίχλη
• η πόλη
• η νύχτα

This helps you remember how adjectives must agree with it.

Because adjectives in Greek must agree with the noun they describe in gender, number, and case.

Here:

• ομίχλη is feminine singular
• so the adjective must also be feminine singular

That gives:

• masculine: πυκνός
• feminine: πυκνή
• neuter: πυκνό

So:

• η ομίχλη είναι πυκνή = the fog is thick/dense

Πιο αργά is an adverb phrase meaning more slowly.

That is because it describes how you drive, not what kind of person you are.

• αργός / αργή / αργό = slow as an adjective
• αργά = slowly as an adverb

So:

• οδηγώ πιο αργά = I drive more slowly

If you said πιο αργός, that would be an adjective and would need to describe a noun, such as:

• Είμαι πιο αργός από σένα. = I am slower than you.

In Modern Greek, a very common way to make a comparative is:

• πιο + adjective/adverb

So:

• πιο αργά = more slowly
• πιο γρήγορα = more quickly
• πιο καλός = better in many everyday contexts, literally more good

This is the regular, practical pattern learners use all the time.

Greek also has some irregular comparative forms in certain words, but πιο is extremely common and useful.

Usually no, not for this meaning.

• πιο αργά = more slowly
• αργότερα usually means later

So:

• Οδηγώ πιο αργά. = I drive more slowly.
• Οδηγώ αργότερα. would sound more like I drive later or I will drive at a later time, depending on context.

This is a very common point of confusion for English speakers because slowly and later are different ideas in Greek.

The comma separates the time clause from the main clause:

• Όταν η ομίχλη είναι πυκνή, = subordinate clause
• οδηγώ πιο αργά. = main clause

This is very natural in Greek, especially when the clause with όταν comes first.

You may also see:

• Οδηγώ πιο αργά όταν η ομίχλη είναι πυκνή.

In that order, the comma is often omitted.

Yes. Greek word order is flexible, although some orders sound more neutral than others.

The original sentence:

• Όταν η ομίχλη είναι πυκνή, οδηγώ πιο αργά.

A very natural alternative is:

• Οδηγώ πιο αργά όταν η ομίχλη είναι πυκνή.

Both mean the same thing. The first version gives slightly more prominence to the condition/time setting: when the fog is thick.

Greek often moves parts of the sentence around for emphasis, rhythm, or style.

Οδηγώ is pronounced roughly o-thee-GO (in Standard Modern Greek), with the stress on the last syllable.

The accent mark shows where the stress falls:

• οδηγώ

That final stressed -ώ is common in some verb forms, especially in the I form of certain verbs:

• μιλώ = I speak
• ρωτώ = I ask
• οδηγώ = I drive

In everyday speech, some verbs may also have alternative forms in usage, but οδηγώ is the standard form to learn here.

Ομίχλη is pronounced approximately o-MEE-khlee.

A few helpful points:

• ο = short o
• μί is stressed
• χ is not like English k or h exactly; it is a throaty sound, like the ch in German Bach or Scottish loch
• λη at the end sounds like lee

So the stress is on the middle syllable:

• ο-ΜΙ-χλη

Yes. Πυκνή ομίχλη is a natural and standard way to say thick fog or dense fog.

The adjective πυκνός / πυκνή / πυκνό often means:

• dense
• thick
• closely packed

So in weather language, πυκνή ομίχλη is a very normal collocation.

Yes. Many Greek adverbs are identical to the neuter singular form of the adjective.

For example:

• αργός = slow (masculine adjective)
• αργή = slow (feminine adjective)
• αργό = slow (neuter adjective)
• αργά = slowly (adverb)

But learners should be careful: Greek adverbs do not always follow one simple pattern in every case, and some are irregular. Still, with common words like αργά, it is very useful to memorize the adverb separately:

• γρήγορα = quickly
• αργά = slowly
• καλά = well

In this sentence, because it modifies the verb οδηγώ, the adverb is exactly what you need.