Šatna je vedle sálu.

Because vedle requires the genitive case.

The basic dictionary form is sál.
After vedle, it changes to sálu.

So:

• sál = hall, auditorium
• vedle sálu = next to the hall

This is something you will see often in Czech: certain prepositions force a particular case, and vedle is one of the prepositions that takes the genitive.

Vedle means next to, beside, or adjacent to.

In this sentence, Šatna je vedle sálu., it means that the cloakroom/changing room is located beside the hall.

A useful thing to remember is:

• vedle + genitive = next to / beside

Examples:

• vedle domu = next to the house
• vedle školy = next to the school

Je is the 3rd person singular form of the verb být, which means to be.

So:

• šatna = the cloakroom / changing room
• je = is
• vedle sálu = next to the hall

Literally: The cloakroom is next to the hall.

Czech often uses je just like English uses is in this kind of location sentence.

It can mean both, depending on context.

Common meanings of šatna include:

• cloakroom
• changing room
• locker room
• dressing room

In a school, sports building, theatre, or event venue, the exact English translation depends on the situation.

So if the meaning has already been given to you, that is probably the best translation for this specific context.

Yes. Czech word order is more flexible than English word order.

The neutral order here is:

• Šatna je vedle sálu.

But other orders are possible, especially for emphasis, such as:

• Vedle sálu je šatna. = There is a cloakroom next to the hall.

Both are grammatical, but they may sound slightly different in focus:

• Šatna je vedle sálu. focuses more naturally on šatna
• Vedle sálu je šatna. focuses more on the location

A rough guide:

• š sounds like sh in shoe
• á is a long vowel, like a longer a
• šatna is roughly SHAT-na
• sálu is roughly saa-loo

More carefully:

• šatna ≈ SHAHT-na
• sálu ≈ SAA-loo

Also, the little mark over á means the vowel is long.

Because Czech has no articles like English a and the.

So šatna can mean:

• a cloakroom
• the cloakroom

And sálu can correspond to:

• of a hall
• of the hall

The exact meaning depends on context. In most real situations, people understand from the situation which specific room or hall is meant.

Not in natural English, but grammatically the Czech structure does involve the genitive, which historically corresponds to something like of the hall.

So word-for-word you could think of it as:

• vedle = beside / next to
• sálu = of the hall

But when translating, you should simply say:

• next to the hall
• beside the hall

Do not translate the case ending mechanically into English.

One clue is its ending: -a nouns are very often feminine in Czech.

So šatna is feminine, and that affects agreement in other contexts.

In this sentence, you do not see much of that, because je is the same for all genders in the present tense. But in other sentences, gender will matter more.

For example, with an adjective:

• malá šatna = a small cloakroom

Here malá shows feminine agreement with šatna.

Here šatna is in the nominative case, because it is the subject of the sentence.

So the sentence structure is:

• Šatna = subject, nominative
• je = verb
• vedle sálu = prepositional phrase, with sálu in the genitive

This is a very common pattern in Czech: [subject in nominative] + [form of být] + [location phrase]

Yes, if you mean hall in the sense of entrance hall or large room, depending on context.

But sál and hala are not always exactly the same:

• sál often means a hall, auditorium, or large room for events
• hala often means a hall, sports hall, industrial hall, or large building space

Both are real words, but they are used in different situations. So sálu is correct here because the original noun is sál.