Если щиколотка болит, лучше посидеть дома и не идти на долгую прогулку.

Both are possible.

• Если щиколотка болит = If the ankle hurts / If your ankle hurts
• Если у тебя болит щиколотка = If your ankle hurts

Russian often leaves out the possessor (my, your, his) when it is obvious from context, especially with body parts. So щиколотка болит sounds natural as a general statement or piece of advice.

Adding у тебя makes it more specifically about your ankle.

Because the subject is щиколотка, which is singular feminine.

• щиколотка болит = the ankle hurts
• ноги болят = the legs hurt

In Russian, the body part is often treated as the grammatical subject:

• Голова болит = My head hurts
• Рука болит = My arm hurts

So the verb agrees with щиколотка, not with an implied person.

Both can refer to the ankle area.

In everyday speech, щиколотка is very common and often refers to the bony ankle area. Лодыжка is also correct and common, and in some contexts may sound a bit more anatomical or neutral.

For a learner, the important thing is:

• both are normal words,
• both can often be translated as ankle.

In this sentence, щиколотка is completely natural.

Russian often uses лучше + infinitive to give general advice:

• Лучше посидеть дома = It’s better to stay home
• Лучше не спорить = It’s better not to argue

This is a very common impersonal structure. It does not need an explicit subject.

You can also say:

• Тебе лучше посидеть дома = You’d better stay home

That version sounds more directly addressed to someone. Without тебе, the advice is more general.

Посидеть is perfective and often means to sit/stay for a while. In this sentence, it suggests a limited, practical action: stay home for some time.

• сидеть = to sit / to be sitting / to stay seated
• посидеть = to sit for a bit / stay for a while

After лучше, both aspects can sometimes appear, but here посидеть sounds natural because it presents the advice as a concrete, bounded action.

So:

• лучше посидеть дома = better stay home for a while
• лучше сидеть дома is possible, but it can sound more general or habitual.

Дома means at home. It is a very common adverb in Russian.

• Я дома = I am at home
• Посидеть дома = stay at home

В доме means in the house/building, focusing more on being physically inside a building.

So:

• дома = at home
• в доме = in the house

In this sentence, дома is the natural choice.

Both can be possible in different contexts, but не идти на прогулку works well here because it means not to go / not to be going on that walk.

Compare:

• идти = to go, to be going
• пойти = to set off, to start going

After лучше, Russian often uses the infinitive to express general advice. Here не идти на долгую прогулку sounds like not go for a long walk.

If you said не пойти, that would focus a bit more on not setting out or not deciding to go. It is not impossible, but не идти is very natural in this sentence.

The phrase идти на прогулку is a standard Russian expression meaning to go for a walk.

So:

• идти на прогулку = to go for a walk
• пойти на прогулку = to go out for a walk

The preposition на is just part of this pattern.

As for долгую:

• прогулка is feminine
• after на with motion, Russian usually uses the accusative
• feminine accusative singular of долгая is долгую

So:

• на долгую прогулку = for a long walk

Russian often leaves out the subject when it is understood from context, especially in advice or general statements.

In English, we often need:

• it’s better for you to stay home and not go...

In Russian, this can be shorter:

• лучше посидеть дома и не идти...

The sentence is understood as general advice to the person whose ankle hurts.

Yes, Если болит щиколотка... is also natural.

Both are correct:

• Если щиколотка болит...
• Если болит щиколотка...

The difference is mainly one of emphasis and word order. Russian word order is flexible.

Very roughly:

• Если щиколотка болит... emphasizes the ankle
• Если болит щиколотка... starts with the verb and can sound slightly more neutral in flowing speech

Both are perfectly understandable and idiomatic.

Yes, often it can.

• Лучше посидеть дома can mean:
  • It’s better to stay home
  • You’d better stay home

The exact English translation depends on tone. Russian лучше + infinitive can range from mild advice to fairly strong recommendation.

So in this sentence, you’d better stay home and not go for a long walk is a very reasonable translation.

Because и не идти на долгую прогулку is joined to посидеть дома as part of the same advice.

The structure is:

• лучше [посидеть дома] и [не идти на долгую прогулку]

These are two coordinated infinitives linked by и, so no comma is needed.

The only comma in the sentence comes after the если clause:

• Если щиколотка болит, ...

That comma separates the condition from the main clause.

It can do either, depending on context, but by itself it sounds like general practical advice.

It means something like:

• If your ankle hurts, it’s better to stay home and not go for a long walk.

Because there is no explicit ты, тебе, or time marker, it sounds broad and general, like advice someone might give in many situations. If you wanted it to sound more directly personal, you could say:

• Если у тебя болит щиколотка, тебе лучше посидеть дома и не идти на долгую прогулку.

That version addresses one person more directly.