La loseta cubre otra casilla.

Because cubre is the conjugated form of the verb cubrir (to cover).

In this sentence, the subject is la loseta (the tile), which is third-person singular, so Spanish uses:

• cubrir = to cover
• cubre = it covers

So La loseta cubre otra casilla literally matches The tile covers another square/cell.

La is the feminine singular definite article, meaning the.

It is used because loseta is a feminine singular noun:

• la loseta = the tile

In Spanish, nouns have grammatical gender, so the article has to match the noun:

• el for masculine singular
• la for feminine singular

Because loseta is grammatically feminine in Spanish. That is simply the gender assigned to the noun, and other words around it must agree with it.

That is why you get:

• la loseta
• not el loseta

A lot of nouns ending in -a are feminine, and loseta follows that common pattern.

In Spanish, otro / otra usually does not take un/una before it.

So Spanish says:

• otra casilla = another square/cell

Not:

• una otra casilla

This is different from English, where another historically comes from an other, but in modern Spanish otra already carries that idea by itself.

Because casilla is a feminine singular noun, and otro has to agree with it.

So the forms are:

• otro for masculine singular
• otra for feminine singular
• otros for masculine plural
• otras for feminine plural

Since it is casilla, you need otra casilla.

Casilla usually means a small square, cell, or space in a grid, board, puzzle, or form.

Depending on context, it could be translated as:

• square
• cell
• space
• sometimes box

So in a game or puzzle context, casilla often refers to one square on a board or grid.

They are not the same thing.

• loseta = a tile, something placed on top or used to cover
• casilla = a square/cell/space in a grid or board

So in this sentence, the idea is that the tile is covering another square.

Because otra already works as a determiner here.

In Spanish, you can say:

• otra casilla = another square
• la otra casilla = the other square

These mean different things:

• otra casilla = one more / a different square
• la otra casilla = the other specific square

So the sentence does not mean the other square; it means another square.

Yes, but the meaning changes.

• La loseta cubre otra casilla = The tile covers another square / a different square
• La loseta cubre la otra casilla = The tile covers the other square

The version with la otra sounds more specific, as if there are two known squares and you mean the second one.

Yes. This is the most neutral and natural order in Spanish:

subject + verb + object

• La loseta = subject
• cubre = verb
• otra casilla = object

Spanish word order is somewhat flexible, but this version is the standard one.

In Spain, a typical pronunciation would be roughly:

la lo-SE-ta KOO-bre O-tra ka-SEE-ya

A few useful notes:

• z in loseta is pronounced like the th in thin in most of Spain.
• c before i in casilla is also pronounced like th in most of Spain.
• ll in casilla is usually pronounced like a y sound in modern Spanish.

So in much of Spain, casilla sounds roughly like ka-SEE-ya.

Yes. Cubrir can mean to cover in a physical sense, and also in more extended meanings depending on context.

For example:

• La manta cubre la cama. = The blanket covers the bed.
• La noticia cubre el tema. = The report covers the topic.

In your sentence, it sounds like a literal or spatial covering: the tile is physically covering another square/cell.

Possibly, depending on the context.

Some related words are:

• baldosa = floor tile
• ficha = token, piece, counter
• pieza = piece
• azulejo = ceramic tile, often wall tile

But loseta is a good choice if the object is specifically tile-like. You should keep loseta if that is the word used in the material you are studying, because near-synonyms often change the exact image or context.