Chefen kräver att resultatet ska förbättras.

Because -en is the definite ending for this common-gender noun.

• en chef = a boss / a manager
• chefen = the boss / the manager

So Chefen kräver ... means The boss demands ...

For the same reason: resultatet is the definite form, meaning the result.

• ett resultat = a result
• resultatet = the result

So att resultatet ska förbättras literally means that the result is to be improved or more naturally that the result should improve / be improved.

Kräver is the present tense of kräva, which means to demand or to require.

• kräva = to demand / require
• kräver = demands / requires

In this sentence, Chefen kräver ... means The boss demands ...

Here att means that and introduces a subordinate clause.

So the structure is:

• Chefen kräver = The boss demands
• att resultatet ska förbättras = that the result should be improved

This is very common in Swedish after verbs like säga (say), tro (think/believe), hoppas (hope), kräva (demand), etc.

Here ska expresses something like is supposed to, is to, or should. In this sentence, it does not simply mean future will.

So resultatet ska förbättras suggests a requirement or expectation:

• the result is to be improved
• the result should be improved

Because the main verb is kräver (demands), ska fits the idea of obligation or requirement.

Because the sentence focuses on the result, not on who will improve it.

• förbättra = to improve something
• förbättras = to be improved / to improve

The -s form is a common Swedish passive. So:

• De förbättrar resultatet = They improve the result
• Resultatet förbättras = The result is improved / The result improves

In your sentence, ska förbättras means should be improved.

Yes, depending on context, förbättras can sometimes feel a bit flexible in English translation.

Swedish förbättras often corresponds to:

• be improved (passive idea)
• improve (intransitive/result-centered idea)

But in this sentence, because Chefen kräver ... sounds like a demand directed at people or processes, English will usually translate it as The boss demands that the result be improved.

This is normal word order in a Swedish subordinate clause.

Structure:

• att = that
• resultatet = subject
• ska = auxiliary/modal verb
• förbättras = main verb

So the clause is built like: that + subject + modal verb + main verb

This is very standard Swedish syntax.

Because Swedish is using a finite clause, not an infinitive clause.

English can say:

• The boss demands that the result be improved

Swedish does the same thing with a full clause:

• Chefen kräver att resultatet ska förbättras

The verb phrase ska förbättras is not an infinitive by itself; it is a modal construction:

• ska = finite verb
• förbättras = infinitive/passive form used after the modal

Normally, no. In this kind of sentence, att should be kept.

So you say:

• Chefen kräver att resultatet ska förbättras.

Leaving out att would sound wrong or at least very unnatural in standard Swedish.

Yes, and the meaning changes slightly.

• Chefen kräver att resultatet ska förbättras
  = The boss demands that the result be improved.
  Focus: the result.

• Chefen kräver att man förbättrar resultatet
  = The boss demands that one/people improve the result.
  Focus: the people doing the action.

Both are possible, but the original sentence is more impersonal and common when the speaker wants to emphasize the required outcome.

Other choices are possible, but they change the nuance.

For example:

• Chefen kräver att resultatet förbättras.
  = The boss demands that the result be improved.
  Slightly more direct/formal.

• Chefen kräver att resultatet måste förbättras.
  = The boss demands that the result must be improved.
  This is possible, but can sound heavier or more explicit than needed.

• Chefen kräver att resultatet ska förbättras.
  = A very natural way to express a demanded or expected future improvement.

So ska is a natural and common choice here.

A careful approximation is:

SHEF-en KREH-ver att reh-sul-TAH-tet skah fur-BET-tras

A few helpful notes:

• ch in chef is pronounced like sh
• ä in kräver is somewhat like the vowel in British bed, though not exactly the same
• ska is usually pronounced with a clear sk sound here
• the stress in resultatet falls mainly on ta
• förbättras has main stress on bät

Swedish pronunciation varies by region, but this will get you close.