Щоб одужати, треба більше відпочивати.

Here щоб means so that, in order to, or simply to in the sense of purpose.

So Щоб одужати = To recover / In order to recover.

It introduces the goal or purpose of the action in the main part of the sentence.

Because after щоб in this kind of short purpose phrase, Ukrainian often uses the infinitive.

• одужати = to recover / to get well
• Щоб одужати = to recover / in order to recover

This is similar to English to recover.

A full clause is also possible in other contexts, but here the infinitive is the most natural and compact form.

This is a question of aspect.

• одужати is perfective: it focuses on the result — to recover, to get well
• одужувати is imperfective: it focuses on the process — to be recovering / to recover in general

In this sentence, одужати is used because the idea is the goal: reaching the state of being well.

So Щоб одужати means in order to get well, not in order to be recovering.

Треба means it is necessary, one needs to, or must / should depending on context.

This is an impersonal construction. Ukrainian often does not state a subject like English you, one, or it.

So:

• треба більше відпочивати = it is necessary to rest more
• more naturally in English: you need to rest more

The person is understood from context. Ukrainian does not need to say you here.

Більше means more.

In this sentence it modifies the verb відпочивати:

• відпочивати = to rest
• більше відпочивати = to rest more

Here більше is an adverb-like comparative form, not an adjective. That is why it does not change for gender, number, or case.

Again, this is about aspect.

• відпочивати = imperfective: to rest, to be resting, to rest repeatedly or for some time
• відпочити = perfective: to have a rest, to rest and complete that action

In треба більше відпочивати, the meaning is general and ongoing: a person needs more rest as a habit or over a period of time.

Using відпочити would sound more like have a rest once / finish resting, which is not the main idea here.

So the sentence means:

• You need to be resting more
• not just You need to rest once

Because Щоб одужати is an introductory subordinate clause of purpose.

Ukrainian normally separates such clauses with a comma:

• Щоб одужати, треба більше відпочивати.

This is similar to English writing:

• To recover, you need to rest more.

If the order is reversed, the comma is still used:

• Треба більше відпочивати, щоб одужати.

Yes.

A very common alternative is:

• Треба більше відпочивати, щоб одужати.

Both versions mean the same thing.

The difference is mostly in emphasis:

• Щоб одужати, треба більше відпочивати.
  Starts with the goal: To recover...
• Треба більше відпочивати, щоб одужати.
  Starts with the main advice: You need to rest more...

Both are natural.

It depends on context.

Треба often means something between:

• need to
• have to
• should

In this sentence, it sounds like practical advice or necessity:

• To recover, you need to rest more.

It usually does not sound as harsh as a strict command like must, unless the context makes it strong.

Щоб is usually pronounced approximately like shchob.

A rough guide:

• щ = a sound like shch together
• о = short o
• б = b

So: shchob

In everyday speech, some speakers pronounce it a bit more simply, but for learners shchob is a good starting point.

Yes, absolutely.

Ukrainian very often leaves out the subject when it is general or obvious from context. In impersonal sentences with треба, this is completely normal.

So Щоб одужати, треба більше відпочивати. is a fully natural complete sentence meaning something like:

• To recover, you need to rest more
• In order to get well, one needs to rest more