La casilla está al final.

Because Spanish normally uses estar for location.

• La casilla está al final = the box/square is located at the end.
• Ser is generally used for identity, origin, time, description, etc.

A very useful rule is:

• use estar for where something is
• except with the location of an event, where Spanish often uses ser

So here, since la casilla is a thing with a location, está is the natural choice.

The accent mark shows both pronunciation and meaning.

• está = he/she/it is or you are (formal), from estar
• esta = this (feminine), as in esta casilla = this box/square

So the accent is important because it distinguishes two different words.

Al is a contraction of a + el.

• a = to / at
• el = the
• a + el = al

So al final literally comes from a el final, but Spanish always contracts that to al.

In this sentence, al final means at the end.

Because the expression is built with the masculine noun final.

• el final = the end
• therefore a + el final = al final

Even though casilla is feminine, that does not affect final here. The phrase al final depends on el final, not on la casilla.

La is the feminine singular definite article, meaning the.

It is used because casilla is a feminine singular noun:

• la casilla = the box / the square / the blank / the booth, depending on context

Spanish often uses articles more regularly than English does, so including la is very normal when referring to a specific item.

Not necessarily. Casilla is a context-dependent word.

Depending on the situation, it can mean things like:

• a box on a form
• a square on a board or grid
• a small booth
• a mailbox/post office box in some contexts

So the exact English word depends on where the sentence appears. The grammar of the sentence stays the same.

Because al final is the normal idiomatic expression for at the end.

In Spanish, learners often want to translate word-for-word from English, but location expressions are often fixed:

• al final = at the end
• al principio = at the beginning

En el final is much less natural in most everyday situations.

Yes, it can.

Al final can mean:

1. at the end in a physical or ordered sense

   • as in this sentence: La casilla está al final.

2. in the end / after all / eventually in a more abstract sense

   • Al final, no fue posible. = In the end, it wasn’t possible.

In your sentence, because it uses está and refers to a location, the meaning is clearly physical or positional: at the end.

Yes. Spanish allows more flexibility than English.

The neutral, straightforward version is:

• La casilla está al final.

But you could also say:

• Al final está la casilla.

That version puts more emphasis on al final or sounds a little more marked. Both are grammatically correct, but the original sentence is the most neutral.

A simple pronunciation guide is:

lah kah-SEE-yah ehs-TAH ahl fee-NAHL

A few notes:

• ll in much of Latin America is pronounced like y
  so casilla sounds like ka-SEE-ya
• the stress in casilla is on si
• the stress in está is on the last syllable: -tá
• the stress in final is on nal

Yes, casilla is feminine singular.

Forms:

• la casilla = the box/square
• las casillas = the boxes/squares

If you made the whole sentence plural, it would be:

• Las casillas están al final.

Notice both the article and the verb change:

• la → las
• está → están

Yes. That is correct and a bit more formal or descriptive.

• La casilla está al final. = simple, natural, everyday
• La casilla se encuentra al final. = the box/square is located at the end

Both are used, but está is usually the more common and direct choice.

It follows a very common pattern:

subject + estar + prepositional phrase

Breaking it down:

• La casilla = subject
• está = verb
• al final = prepositional phrase showing location

So this is a useful model you can reuse:

• El banco está aquí. = The bench is here.
• La tienda está cerca. = The store is nearby.
• El baño está al fondo. = The bathroom is at the back.