Βάλε το ποτήρι πάνω στο σουβέρ, γιατί το τραπέζι είναι ξύλινο και δεν θέλω να μείνει λεκές.

Βάλε is the singular imperative of βάζω, meaning put.

More specifically, it is the aorist imperative, which is very common for a single, complete action:

• Βάλε το ποτήρι... = Put the glass...
• plural: Βάλτε το ποτήρι... = Put the glass... when speaking to more than one person, or politely to one person

Greek often uses the aorist imperative for one-time commands like put it there, open the door, write your name, and so on.

Greek uses the definite article much more regularly than English. Here το ποτήρι means the glass.

Also, ποτήρι is a neuter noun, so its article is το in the singular.

In this sentence, το ποτήρι is the direct object of Βάλε. For neuter nouns like ποτήρι, the nominative and accusative forms are the same, so you do not see a change in the noun itself.

πάνω στο means on / onto / on top of, depending on context.

It breaks down like this:

• πάνω = above / on top
• στο = σε + το = on/to the

So:

• πάνω στο σουβέρ = on the coaster

With a verb of placement like Βάλε, English may translate this as either on the coaster or onto the coaster.

Because στο is the contracted form of σε το.

This is extremely common in Modern Greek:

• σε + το = στο
• σε + τη(ν) = στη(ν)
• σε + τον = στον

So πάνω στο σουβέρ is literally something like on the coaster, with στο already containing the article το.

σουβέρ means coaster.

It is a loanword, and in everyday Modern Greek it is usually treated as indeclinable, meaning the noun itself often stays the same. The article shows the gender/number/case:

• το σουβέρ
• στο σουβέρ

So even though the noun does not visibly change, the article still does the grammatical work.

γιατί can mean both why and because.

The meaning depends on context:

• Γιατί έφυγες; = Why did you leave?
• Έφυγα γιατί νύσταζα. = I left because I was sleepy.

In your sentence, it introduces a reason clause, so it means because:

• ..., γιατί το τραπέζι είναι ξύλινο...
• ..., because the table is wooden...

Because ξύλινο must agree with τραπέζι, and τραπέζι is a neuter singular noun.

Greek adjectives agree with the noun in gender, number, and case:

• masculine: ξύλινος
• feminine: ξύλινη
• neuter: ξύλινο

So:

• το τραπέζι είναι ξύλινο = the table is wooden

Here λεκές means a stain, not the stain, so Greek naturally leaves it without the definite article.

So:

• να μείνει λεκές = for a stain to be left / for there to be a stain left

If you added ένας, you would be stressing the idea of one stain / a stain more explicitly:

• να μείνει ένας λεκές

But in natural Greek, the bare noun λεκές is very normal here.

Also note that λεκές is the subject of μείνει, so it appears in the nominative.

This is an aspect difference.

• να μείνει = aorist subjunctive of μένω
• να μένει = present subjunctive

In this sentence, να μείνει λεκές focuses on the result: the speaker does not want a stain to be left behind. That makes the aorist form natural.

So:

• δεν θέλω να μείνει λεκές = I don’t want a stain to be left

If you used να μένει, it would sound more like an ongoing or repeated situation, which is not the main idea here.

να introduces a subordinate clause with the subjunctive.

After verbs like θέλω, Greek normally uses να + verb:

• Θέλω να φύγω = I want to leave
• Θέλω να έρθεις = I want you to come
• Δεν θέλω να μείνει λεκές = I don’t want a stain to remain / be left

So να is a key word that helps build this kind of want / wish / intention / possibility structure.

That is a very good question, because both patterns are possible, but they are structured differently.

Your sentence says:

• δεν θέλω να μείνει λεκές
• literally: I do not want a stain to remain

Here the main verb is negative: δεν θέλω.

Another possible way to express a similar idea is:

• θέλω να μη μείνει λεκές
• I want no stain to remain

There, the main verb is positive, and the subordinate clause is negative with μη(ν).

So:

• δεν θέλω να μείνει λεκές = I don’t want a stain left
• θέλω να μη μείνει λεκές = I want no stain to be left

They are close in meaning, but the focus is slightly different. The version in your sentence is completely natural.

Greek word order is more flexible than English, although the version you have is very natural and neutral.

For example, Greek could also say things like:

• Βάλε το ποτήρι στο σουβέρ...
• Γιατί είναι ξύλινο το τραπέζι...

But these can create slightly different emphasis.

Your sentence:

• Βάλε το ποτήρι πάνω στο σουβέρ, γιατί το τραπέζι είναι ξύλινο και δεν θέλω να μείνει λεκές.

is a normal, straightforward way to say it. The order helps the sentence sound clear and natural, without special emphasis.