Лестничная площадка свободна.

In Russian, the verb to be is normally omitted in the present tense.

So:

• Лестничная площадка свободна. = The landing is free.

But in the past or future, Russian does use forms of быть:

• Лестничная площадка была свободна. = The landing was free.
• Лестничная площадка будет свободна. = The landing will be free.

This is one of the most common differences from English.

This is a very important grammar point.

Свободна is the short form of the adjective свободная.

Russian often uses:

• the full form of an adjective when it describes a noun directly
• the short form when the adjective is the main predicate of the sentence

Compare:

• свободная площадка = a free / available landing
  Here the adjective directly modifies the noun.

• площадка свободна = the landing is free / available
  Here the adjective is saying the state of the subject.

So in your sentence, свободна is used because it means is free.

Because the subject, лестничная площадка, is feminine singular.

The short form of свободный changes by gender and number:

• masculine: свободен
• feminine: свободна
• neuter: свободно
• plural: свободны

Examples:

• Стул свободен. = The chair is free.
• Комната свободна. = The room is free.
• Место свободно. = The seat is free.
• Комнаты свободны. = The rooms are free.

It is in the nominative case.

In this sentence, лестничная площадка is the subject of the sentence, and subjects are normally in the nominative.

You can tell from the dictionary-like form:

• лестничная площадка = nominative singular

So the structure is basically:

• [subject] + [predicate adjective]
• Лестничная площадка + свободна

Because лестничная площадка means a specific part of a staircase area: the landing.

The words are:

• лестница = staircase / stairs
• площадка = platform / small area / landing

So лестничная площадка literally means something like stair platform, but the natural English translation is stair landing or just landing.

This is a set phrase you will see in buildings, housing, and safety notices.

Лестничная is an adjective meaning stair- / staircase-related.

It comes from лестница (staircase), and it agrees with площадка, which is feminine singular:

• лестничный — masculine
• лестничная — feminine
• лестничное — neuter
• лестничные — plural

So:

• лестничная площадка = stair landing
• literally, staircase-related platform/area

The stress is:

• лЕстничная
• площАдка
• свободнА

A rough pronunciation guide:

• лЕстничная ≈ LYEST-ni-chna-ya
• площАдка ≈ plo-SHAT-ka
• свободнА ≈ sva-bad-NA

A few helpful notes:

• In normal speech, unstressed о often sounds closer to a.
• The щ in площадка is a soft long sh-like sound.
• The stress in свободна is on the final -а.

Yes, Russian word order is more flexible than English, but the neutral, most natural order here is:

• Лестничная площадка свободна.

You could also say:

• Свободна лестничная площадка.

But that sounds more marked or literary, and it may put extra focus on свободна.

For most learners, the standard order subject + predicate is the safest choice.

It depends on context.

In a sentence like this, свободна usually means something like:

• available
• unoccupied
• clear
• not blocked

For a stair landing, the idea is usually that the area is clear/open, not taken up or obstructed.

So the exact English wording may vary depending on the situation, but the Russian adjective свободен / свободна / свободно / свободны often describes something being available or not occupied.

Grammatically, you may sometimes hear full forms in predicate position, but in this kind of simple statement about a current state, Russian strongly prefers the short form:

• Лестничная площадка свободна.

Using свободная here would usually sound less natural in standard usage.

As a general rule:

• full form = attribute, description attached to a noun
• short form = predicate, state of the subject

So for learners, the best pattern to remember is:

• Комната свободна.
• Дверь открыта.
• Магазин закрыт.

Yes, absolutely.

This type of short, compact sentence is very common in:

• building notices
• safety announcements
• hotel or apartment contexts
• emergency instructions

Russian often uses brief statements like this to describe the state of a place or object:

• Дверь закрыта. = The door is closed.
• Проход свободен. = The passage is clear.
• Место занято. = The seat is occupied.

So Лестничная площадка свободна. sounds perfectly natural in an informational or practical context.