Προτού βάλω το ποτήρι στο τραπέζι, το γυαλίζω με ένα καθαρό πανί.

Προτού means before when it introduces a whole clause, as it does here: Προτού βάλω... = Before I put...

A learner will often also see πριν in the same kind of sentence:

• Πριν βάλω το ποτήρι...

That is also natural. Προτού can sound a bit more formal or literary than πριν, but both are common and correct.

Because after προτού, Greek uses a subjunctive-type form, and here that form is βάλω.

• βάζω = I put / I am putting, as a general or ongoing action
• βάλω = the perfective form, focusing on one complete act of putting

So Προτού βάλω το ποτήρι... means Before I put the glass..., with the idea of one completed placing action.

You do not use θα here, because after conjunctions like προτού, Greek normally does not express this with a future marker the way English might think of it.

Greek often leaves out subject pronouns because the verb ending already shows the subject.

Here:

• βάλω = I put / I place
• γυαλίζω = I polish / I am polishing

So the I is built into the verb form. You could add εγώ for emphasis, but it is not necessary:

• Προτού βάλω..., εγώ το γυαλίζω...

That would sound emphatic, like I polish it...

No. Το is doing different jobs in different places.

In this sentence:

• το ποτήρι = the glass
  Here το is the definite article: the

• το γυαλίζω = I polish it
  Here το is a direct object pronoun: it

• στο τραπέζι = on/to the table
  Here the το is again the article the, but combined with σε to make στο

So the form is the same, but the grammar function changes.

Because weak object pronouns in Greek usually come before a finite verb.

So:

• το γυαλίζω = I polish it
• not γυαλίζω το

This is very normal Greek word order for object pronouns. English speakers often want to place the pronoun after the verb, but Greek usually puts it before.

Στο is a contraction of:

• σε + το = στο

The preposition σε is very broad in Greek. Depending on context, it can correspond to English:

• in
• at
• to
• on

So:

• στο τραπέζι literally has σε + το τραπέζι
• with βάζω and an object like τραπέζι, English naturally says on the table

Greek often does not need a separate word like on here. The context makes the meaning clear.

Yes. All three nouns here are neuter singular:

• το ποτήρι = the glass
• το τραπέζι = the table
• το πανί = the cloth

That affects the article and adjective forms:

• το ποτήρι
• το τραπέζι
• ένα καθαρό πανί

Notice how καθαρό is also neuter singular, agreeing with πανί.

This is a useful pattern: many Greek neuter nouns end in -ι.

Here γυαλίζω means to polish, to shine, or to make shiny.

So:

• το γυαλίζω = I polish it

It comes from γυαλί (glass), but as a verb it does not mean to glass. In everyday Greek, γυαλίζω is the normal verb for polishing or making something shiny.

Here με means with, in the sense of using something as a tool or means.

So:

• με ένα καθαρό πανί = with a clean cloth

This is the standard way to express the instrument used to do an action:

• γράφω με μολύβι = I write with a pencil
• κόβω με μαχαίρι = I cut with a knife

Because ένα means a / one, so the sentence is talking about a clean cloth, not a specific cloth already known to the listener.

• με ένα καθαρό πανί = with a clean cloth
• με το καθαρό πανί = with the clean cloth

Using το would suggest a particular cloth that has already been identified.

It can mean either, depending on context.

The Greek present tense often covers both:

• simple present: I polish
• present continuous: I am polishing

So το γυαλίζω could mean:

• I polish it as a general habit, or
• I am polishing it right now

In this sentence, the most natural reading is probably a general routine:

• Before I put the glass on the table, I polish it with a clean cloth.

Because Greek is paying attention to aspect, not just time.

• βάλω presents the action as one complete event: putting the glass on the table
• γυαλίζω presents the action more as an ongoing or general action: polishing it

So the sentence combines:

• a single completed action in the subordinate clause
• a present/habitual action in the main clause

This is very normal in Greek. English speakers often expect both verbs to line up more closely, but Greek chooses the form based on how each action is viewed.