Plansza leży na stole.

Because na changes case depending on meaning.

• na stole = on the table in a static location, so stół takes the locative case: stole
• na stół = onto the table with movement toward it, so stół takes the accusative case: stół

So in Plansza leży na stole, nothing is moving; the board is already there, so na stole is correct.

Plansza is in the nominative case, because it is the subject of the sentence — the thing that is doing the lying.

In this sentence:

• plansza = subject, nominative
• na stole = location phrase, with stół in the locative

Polish often prefers a more specific verb for position or posture where English might simply use is.

So:

• Plansza jest na stole = The board is on the table
• Plansza leży na stole = The board is lying on the table

The version with leży sounds more natural when talking about something resting flat or lying somewhere.

Leży is the 3rd person singular present tense of the verb leżeć (to lie, to be lying).

It matches plansza, which is singular.

A few present-tense forms of leżeć are:

• ja leżę = I am lying
• ty leżysz = you are lying
• on / ona / ono leży = he / she / it is lying
• my leżymy
• wy leżycie
• oni / one leżą

Plansza is feminine.

A very common clue is that nouns ending in -a are often feminine in Polish.

That matters because adjectives and past-tense verbs would have to agree with it. For example:

• duża plansza = a big board
• plansza leżała na stole = the board was lying on the table

Yes. Polish word order is fairly flexible.

The neutral order here is:

• Plansza leży na stole.

But you could also say:

• Na stole leży plansza.

Both are correct. The difference is mainly emphasis:

• Plansza leży na stole focuses first on the board
• Na stole leży plansza focuses first on the location

A rough pronunciation guide is:

• Plansza ≈ PLAN-sha
• leży ≈ LEH-zhih
• na ≈ nah
• stole ≈ STO-leh

A few useful sound notes:

• sz sounds like English sh
• ż sounds like the s in measure
• Polish y is not the same as English ee; it is a shorter, more central sound

Because Polish does not use articles like a or the.

So Plansza leży na stole can mean:

• A board is lying on the table
• The board is lying on the table

The exact meaning depends on context.

Here na means on.

It is a very common preposition in Polish, but it does not always work exactly like English on. It can be used with different cases:

• na stole = on the table, at the table, on top of the table area (location)
• na stół = onto the table (movement)

So you always need to learn both the preposition and the case pattern it uses.

Yes, you could, and it would be understandable.

But there is a nuance:

• Plansza jest na stole = the board is on the table
• Plansza leży na stole = the board is lying on the table

The version with leży is more vivid and natural if the object is physically resting there, especially flat.

Yes, for the singular locative, stół becomes stole.

Some common forms are:

• stół = nominative singular
• stołu = genitive singular
• stół = accusative singular
• stołem = instrumental singular
• stole = locative singular

This vowel change is normal for this noun and just has to be learned as part of its declension.