Πριν φύγεις, κοίτα αν το κουμπί στο παλτό σου είναι καλά ραμμένο.

It is the 2nd person singular imperative of κοιτάω / κοιτώ.

Literally, κοίτα means look, but in this sentence it is more natural to translate it as check:

• κοίτα αν... = check whether / see if...

So here it means something like:

• Before you leave, check whether...

It is addressed to one person informally.
If you were speaking to more than one person, or using formal you, you would normally say κοιτάξτε.

Because after πριν meaning before, Greek commonly uses the aorist subjunctive-type form for a single action viewed as complete.

So:

• πριν φύγεις = before you leave

Here φύγεις comes from φεύγω (to leave / go away), but it is not the ordinary present form.

Why not φεύγεις?

• φεύγεις = you are leaving / you leave
• φύγεις = the form Greek uses here for before you leave

The idea is not ongoing action, but the event of leaving as one whole action.

No. Even though it uses the aorist stem, here it is not past tense.

In Modern Greek, forms like φύγεις, πας, δεις, βρεις often appear in environments such as:

• να φύγεις
• αν φύγεις
• πριν φύγεις

So in this sentence, φύγεις means leave, not left.

Yes. Πριν φύγεις and πριν να φύγεις are both possible.

In everyday Greek, πριν φύγεις is very common and natural.
Adding να can sound a little fuller, but the meaning is the same:

• Πριν φύγεις...
• Πριν να φύγεις...

Both mean before you leave.

Here αν means whether.

English often says:

• check if the button...

but that if really means whether, not a condition. Greek uses αν for this kind of indirect yes/no question:

• κοίτα αν... = check whether... / see if...

So this is not a conditional sentence like If you leave, ...
It is an indirect question: Is the button well sewn or not?

στο is a contraction of:

• σε + το = στο

The preposition σε can mean in, on, at, to, depending on context.

So:

• στο παλτό σου = on your coat / literally on the coat your

In this sentence, στο is best understood as on:

• the button on your coat

In Greek, possessive words like μου, σου, του, της, μας, σας, τους usually come after the noun.

So:

• το παλτό σου = your coat
• literally: the coat your

This is completely normal Greek word order.

So the pattern is:

• το βιβλίο μου = my book
• το σπίτι σου = your house
• το παλτό σου = your coat

Greek uses the definite article very often, often more regularly than English.

Here:

• το κουμπί = the button
• το παλτό σου = your coat

Even with possessives, Greek normally keeps the article:

• το παλτό σου, not just παλτό σου

So for an English speaker, one useful rule is:
when in doubt, Greek often wants the article where English might not focus on it as much.

ραμμένο is the passive participle of ράβω (to sew).

So:

• ραμμένο = sewn

With είναι, it describes a resulting state:

• είναι ραμμένο = it is sewn

In this sentence:

• είναι καλά ραμμένο = it is well sewn / properly sewn

For a button, this naturally means securely sewn on.

Because it agrees with το κουμπί.

• κουμπί is neuter singular
• so the participle must also be neuter singular
• therefore: ραμμένο

Compare:

• ο γιακάς είναι ραμμένος = the collar is sewn
• η τσέπη είναι ραμμένη = the pocket is sewn
• το κουμπί είναι ραμμένο = the button is sewn

Greek adjectives and participles usually agree in gender and number with the noun they describe.

Because καλά is functioning as an adverb here: well / properly.

It modifies ραμμένο:

• καλά ραμμένο = well sewn / properly sewn

Why not καλό?

• καλό is an adjective meaning good
• but here Greek needs an adverb, not an adjective

What about καλώς?

• καλώς exists, but in many everyday contexts it sounds more formal or less natural
• καλά is the normal everyday choice

Not in the same way English does.

English often says:

• the button is sewn on well

Greek says:

• το κουμπί ... είναι καλά ραμμένο

The idea of attachment is understood from ραμμένο in this context, and the location is already given by:

• στο παλτό σου = on your coat

So Greek does not need a separate little word matching English on after sewn.

Yes, you could.

Both are possible, but they feel slightly different:

• το κουμπί στο παλτό σου = the button on your coat
• το κουμπί του παλτού σου = the button of your coat

The version with στο sounds very natural and everyday, because it presents the button as something located on the coat.

The version with του παλτού σου is also correct, but it sounds a bit more like a possession/relationship phrase: the coat's button.

Yes. παλτό is a borrowed noun and is commonly treated as indeclinable in everyday Modern Greek.

So the noun itself stays the same:

• το παλτό
• στο παλτό
• από το παλτό

The article shows the grammar, while παλτό itself usually does not change form.

You would change the singular forms to plural/formal ones:

• Πριν φύγετε, κοιτάξτε αν το κουμπί στο παλτό σας είναι καλά ραμμένο.

Changes:

• φύγεις → φύγετε
• κοίτα → κοιτάξτε
• σου → σας

So the structure stays the same; only the you forms change.