El peón está a punto de llegar a otra casilla.

Because estar is used in the expression estar a punto de + infinitive, which means to be about to + verb.

So:

• está a punto de llegar = is about to arrive / is about to reach

You cannot use ser here. Es a punto de llegar would be incorrect.

A punto de + infinitive means just about to, on the point of, or about to do something.

Examples:

• Estoy a punto de salir. = I’m about to leave.
• Estamos a punto de empezar. = We’re about to begin.

In your sentence, está a punto de llegar means the pawn is very close to reaching another square.

Because the fixed expression is estar a punto de + infinitive.

So the pattern is:

• estar
• a punto de
• infinitive verb

For example:

• Está a punto de ganar.
• Estoy a punto de caerme.

The de is part of the structure, so it must be there.

The verb llegar usually takes a before the destination.

So:

• llegar a casa
• llegar al final
• llegar a Madrid
• llegar a otra casilla

That a is part of how the verb works. It is not the same as the personal a used with people.

Here, peón means pawn in chess.

The word peón can also mean labourer or worker in other contexts, so the exact meaning depends on the situation.

Since the sentence mentions casilla, which is a chessboard square, peón clearly means the chess piece.

In Spanish, articles like el, la, los, and las are used more often than in English.

So Spanish often says:

• El peón
• La reina
• El rey

where English might simply say:

• The pawn
• or sometimes just pawn, depending on context

Using el here sounds natural and complete in Spanish.

Otra casilla means another square.

• otra = another / other
• la otra = the other

So there is an important difference:

• otra casilla = some other square, another one
• la otra casilla = the other square, a specific one already known

In your sentence, otra casilla is the natural choice if the idea is simply that the pawn is about to move to a different square.

Casilla is the normal word for a square on a board, especially in games like chess.

So in this context:

• casilla = square on the chessboard

Other words would sound less natural here:

• cuadrado usually means a geometric square shape
• espacio means space, area, or room

For chess, casilla is the right word.

In Spanish, words like otro / otra normally come before the noun.

So:

• otra casilla
• otro peón
• otra vez

This is just the normal word order.

It can be understood as either, depending on how naturally you want to translate it into English.

• arrive at another square
• reach another square

In this chess context, reach often sounds more natural in English, but arrive at is also close to the Spanish verb llegar.

The accent mark shows the stress: pe-ÓN.

Without the written accent, Spanish spelling rules would suggest a different stress pattern. The accent tells you the stress falls on the last syllable.

So it is pronounced roughly:

• pe-ON

not PE-on.

Yes, but it means something slightly different.

• El peón está a punto de llegar a otra casilla = The pawn is just about to reach another square
• El peón va a llegar a otra casilla = The pawn is going to reach another square

Está a punto de is more immediate. It suggests the action is about to happen very soon. Va a llegar is more general and less dramatic.

It strongly sounds like chess because of the combination of:

• peón
• casilla

Those two words together strongly suggest a board game, especially chess.

Outside that context, peón could mean a worker and casilla could mean a small box or slot on a form, but in this sentence the most natural interpretation is definitely chess.