Προχωράς ευθεία μέχρι το φανάρι και μετά στρίβεις αριστερά.

In Greek, the present tense is very commonly used for instructions, directions, and step-by-step guidance.

So:

• Προχωράς ευθεία = You go straight / You keep going straight
• μετά στρίβεις αριστερά = then you turn left

This is similar to English directions like:

• You go straight, then you turn left

It does not necessarily mean the action is happening right now. In context, it works like an instruction.

Both verbs are 2nd person singular.

• προχωράς = you proceed / you go on
• στρίβεις = you turn

This means the speaker is addressing one person informally.

If the speaker were talking to:

• more than one person, or
• one person politely

they would usually say:

• Προχωράτε ευθεία μέχρι το φανάρι και μετά στρίβετε αριστερά.

So the sentence you have is the informal singular version.

Greek usually drops subject pronouns when they are not needed, because the verb ending already shows who the subject is.

For example:

• προχωράς already tells you it means you
• στρίβεις also already tells you you

So εσύ is unnecessary unless the speaker wants emphasis or contrast.

For example:

• Εσύ προχωράς ευθεία, όχι εγώ.
  = You go straight, not me.

In normal directions, leaving out the pronoun is the natural choice.

Προχωράς comes from προχωράω / προχωρώ, which basically means:

• move forward
• proceed
• continue on

In directions, προχωράς ευθεία means something like:

• go straight
• keep going straight
• continue straight ahead

You could also hear πηγαίνεις ευθεία, which also means you go straight. The difference is subtle:

• προχωράς often has the sense of continuing forward
• πηγαίνεις is the more general go

Both are natural in directions.

Here ευθεία is being used adverbially, meaning:

• straight
• straight ahead

So Προχωράς ευθεία means You go straight.

This is very common in Greek: a word that can also be an adjective or noun may be used as an adverb in certain expressions.

In directions, ευθεία is a standard way to say:

• straight
• straight on

You may also hear ίσια in everyday speech with a similar meaning.

μέχρι means:

• until
• up to
• as far as

So:

• μέχρι το φανάρι = up to the traffic light / until the traffic light

In this sentence, it tells you the limit of the movement:

• keep going straight until you reach the traffic light

Here το φανάρι is in the accusative case, which is normal after μέχρι when it is followed by a noun phrase in Modern Greek.

So:

• μέχρι το φανάρι = until the traffic light

The noun is:

• nominative: το φανάρι
• accusative: το φανάρι

In this particular noun, nominative and accusative look the same, so you do not see a form change. But grammatically, this is the object of μέχρι.

In everyday Modern Greek, το φανάρι very often means:

• traffic light

That is almost certainly what it means in this sentence.

The word can also have older or more literal meanings such as:

• lamp
• lantern

But in directions like this, μέχρι το φανάρι normally means:

• until you get to the traffic light

Here μετά means:

• then
• after that

So:

• και μετά στρίβεις αριστερά = and then you turn left

A useful distinction:

• μετά on its own often means then / afterwards
• μετά από
  • noun usually means after

For example:

• Μετά φεύγω. = Then I leave.
• Μετά από μία ώρα φεύγω. = I leave after one hour.

In your sentence, μετά is simply sequencing the directions.

Because αριστερά here is functioning as an adverb, not as an adjective.

• στρίβεις αριστερά = you turn left

It tells you how / in what direction you turn.

Compare:

• η αριστερή πλευρά = the left side
  Here αριστερή is an adjective.
• στρίβω αριστερά = I turn left
  Here αριστερά is adverbial.

This is one of the most common direction expressions in Greek.

The given word order is very natural, but Greek word order is fairly flexible.

Your sentence:

• Προχωράς ευθεία μέχρι το φανάρι και μετά στρίβεις αριστερά.

A speaker could also say things like:

• Προχωράς μέχρι το φανάρι ευθεία και μετά στρίβεις αριστερά.
• Μετά στρίβεις αριστερά.

But the original version sounds very natural and clear for directions.

In general, Greek allows some movement of words for:

• emphasis
• rhythm
• clarity

Still, the sentence you have is probably the most neutral and standard phrasing.

A rough pronunciation guide is:

pro-ho-RAS ef-THEE-a ME-hri to fa-NA-ri ke me-TA STREE-vis a-ri-ste-RA

A few helpful notes:

• χ in προχωράς is a Greek sound with no exact English equivalent; it is a rough throat sound.
• θ in ευθεία sounds like th in think
• The stressed syllables are marked by the written accents:
  • προχωράς
  • ευθεία
  • μετά
  • στρίβεις
  • αριστερά

Paying attention to the written accent marks will help your pronunciation a lot.

You would use the 2nd person plural forms:

• Προχωράτε ευθεία μέχρι το φανάρι και μετά στρίβετε αριστερά.

So:

• προχωράς / στρίβεις = singular informal
• προχωράτε / στρίβετε = plural or polite singular

This is very useful in real life, because when speaking to a stranger, Greek often uses the plural for politeness.