יציבה טובה עוזרת לניידות.

In Hebrew, adjectives usually come after the noun they describe.

So:

• יציבה טובה = good posture
• literally: posture good

This is the normal Hebrew order. English does the opposite: good posture.

Also, the adjective has to match the noun in:

• gender
• number
• definiteness

Since יציבה is feminine singular, the adjective is טובה, which is also feminine singular.

Because the subject, יציבה טובה, is treated as feminine singular.

In Hebrew, present-tense verbs agree with the subject in gender and number:

• עוזר = masculine singular
• עוזרת = feminine singular
• עוזרים = masculine plural
• עוזרות = feminine plural

Since יציבה is feminine, the sentence uses עוזרת.

עוזרת is the present tense form of the verb לעזור (to help).

In Hebrew, the present tense often covers meanings like:

• helps
• is helping
• does help

In this sentence, it has a general meaning:

• Good posture helps mobility.

So it is not talking about one specific moment only; it is stating a general fact.

The verb לעזור (to help) usually takes ל־ before the thing or person being helped.

So Hebrew says:

• לעזור למישהו / למשהו
• literally: to help to someone / to something

That is why you get:

• עוזרת לניידות = helps mobility

This is just how the verb works in Hebrew.
English says help something, but Hebrew says help to something in structure.

Because the sentence is speaking generally, not about one specific posture or one specific mobility.

• יציבה טובה = good posture / a good posture
• היציבה הטובה = the good posture
• ניידות = mobility
• הניידות = the mobility

In general statements, Hebrew often leaves nouns indefinite, just like English often does:

• Good posture helps mobility
• not necessarily The good posture helps the mobility

Here, יציבה is a noun, meaning posture.

But this form can also be recognized as an adjective form in other contexts, because יציבה can also relate to the idea of being stable/steady in feminine form.

In this sentence, though, the structure makes it clear:

• יציבה טובה = good posture

So here it functions as a noun.

Yes. עוזרת can also be a noun meaning female helper or assistant.

For example:

• היא עוזרת לי = She helps me
  Here עוזרת is a verb.

• היא עוזרת במשרד = She is an assistant in the office
  Here עוזרת could be understood as a noun, depending on context.

In your sentence, עוזרת is clearly a verb, because it connects the subject יציבה טובה with לניידות.

The sentence follows a very common Hebrew pattern:

• Subject: יציבה טובה
• Verb: עוזרת
• Prepositional complement: לניידות

So the structure is:

• Good posture
  • helps
    • mobility

That is very close to normal English word order.

Inside the subject, though, Hebrew differs from English:

• English: good posture
• Hebrew: posture good

A rough pronunciation is:

ye-tzi-VAH to-VAH o-ZE-ret le-na-ya-DUT

A few notes:

• יציבה → stress on the last syllable: va
• טובה → stress on the last syllable: va
• עוזרת → stress on ZE
• ניידות → stress on the last syllable: dut

If you want a smoother whole-sentence rhythm:

ye-tzi-VAH to-VAH o-ZE-ret le-na-ya-DUT

Not exactly. ניידות is closer to mobility than to movement.

• movement is more general and can mean physical motion
• mobility often means the ability to move well or easily

So in a health, body, or physical-function context, ניידות is a very natural word for mobility.

That is why יציבה טובה עוזרת לניידות sounds like a general statement about physical functioning.

Yes. Hebrew has other ways to express the same idea. For example:

• יציבה טובה מסייעת לניידות
  מסייעת also means helps/assists, but sounds a bit more formal.

• יציבה טובה תורמת לניידות
  This means Good posture contributes to mobility.

But יציבה טובה עוזרת לניידות is perfectly natural and easy to understand.

Here are the base forms:

• יציבה — a noun meaning posture
• טוב — the basic adjective meaning good
  In the sentence it becomes טובה to match the feminine noun.
• לעזור — to help
  In the sentence it appears as עוזרת.
• ניידות — mobility

This is useful because in Hebrew, the form you see in a sentence often changes to match gender, number, or sentence structure.