Meine Schwester fegt die Küche, während ich den Balkon sauber mache.

Because Schwester is a feminine noun in German: die Schwester.

The possessive mein- changes its ending to match the noun’s gender, number, and case. In the nominative feminine singular, it becomes meine.

So:

• mein Bruder = my brother
• meine Schwester = my sister

In this sentence, meine Schwester is the subject of the first clause, so nominative is needed.

They are in different grammatical genders, and both are being used in the accusative case because they are the direct objects of the verbs.

• die Küche is feminine
• der Balkon is masculine

In the accusative:

• feminine die stays die
• masculine der changes to den

So:

• die Küche → die Küche
• der Balkon → den Balkon

That is why the sentence has:

• fegt die Küche
• mache den Balkon sauber

Because they are the things directly affected by the actions.

• fegen = to sweep
  → what is being swept? die Küche
• sauber machen = to clean / make clean
  → what is being cleaned? den Balkon

In German, the direct object usually takes the accusative case.

So the basic pattern is:

• jemand fegt etwas
• jemand macht etwas sauber

Fegt is the 3rd person singular form of fegen, which means to sweep.

So:

• ich fege = I sweep
• du fegst = you sweep
• er/sie/es fegt = he/she/it sweeps

In this sentence, the subject is meine Schwester, which is third person singular, so the verb is fegt.

A natural English translation is often My sister is sweeping the kitchen, even though German is just using the present tense.

Because sauber machen is a common German expression meaning to clean or literally to make clean.

It works like this:

• sauber = clean
• machen = to make / do

Together: etwas sauber machen = to clean something

In a main clause, machen is the conjugated verb, and sauber stays near the end:

• Ich mache den Balkon sauber.

So in your sentence:

• ich den Balkon sauber mache

because that whole part is a subordinate clause, and the verb mache moves to the end.

Yes, essentially.

You may see both:

• sauber machen
• saubermachen

Both can be correct, depending on style and context. In everyday writing, the separated version sauber machen is very common and easy for learners to recognize.

In conjugated sentences, you will often notice the two parts split anyway:

• Ich mache das Bad sauber.

And in the infinitive:

• Ich muss das Bad sauber machen.

So for a learner, it is best to understand it as a verbal expression meaning to clean.

Because während is a subordinating conjunction.

Subordinating conjunctions introduce subordinate clauses, and in German subordinate clauses, the conjugated verb goes to the end.

So:

• main clause: Ich mache den Balkon sauber.
• subordinate clause with während: während ich den Balkon sauber mache

That final mache is exactly what we expect after während.

Other common subordinating conjunctions that also send the verb to the end are:

• weil = because
• dass = that
• wenn = if/when
• obwohl = although

Because in German, subordinate clauses are normally separated from the main clause by a comma.

Since während ich den Balkon sauber mache is a subordinate clause introduced by während, a comma is required:

• Meine Schwester fegt die Küche, während ich den Balkon sauber mache.

German comma rules are often stricter than English ones, so this comma is not optional.

Here, während means while.

It shows that the two actions happen at the same time:

• my sister is sweeping the kitchen
• I am cleaning the balcony

So the sentence describes simultaneous actions.

Be aware that während can also be used as a preposition in other contexts, but here it is clearly a conjunction introducing a clause:

• während ich den Balkon sauber mache = while I clean the balcony

German very often uses the present tense for actions happening right now.

So:

• Meine Schwester fegt die Küche
  can mean
• My sister sweeps the kitchen or, more naturally in context, My sister is sweeping the kitchen

Likewise:

• ich den Balkon sauber mache
  can mean
• I clean the balcony or I am cleaning the balcony

German does not need a special progressive form like English is doing.

Yes.

You can also say:

Während ich den Balkon sauber mache, fegt meine Schwester die Küche.

That is equally correct.

But when the subordinate clause comes first, the main clause follows the verb-second rule, so the verb comes immediately after the subordinate clause:

• Während ich den Balkon sauber mache, fegt meine Schwester die Küche.

Notice that fegt comes before meine Schwester in the second clause.

Because this is a subordinate clause after während.

In an independent main clause, German usually keeps the conjugated verb in the second position:

• Ich mache den Balkon sauber.

But in a subordinate clause, the conjugated verb goes to the end:

• während ich den Balkon sauber mache

So the word order changes because of the clause type, not because the meaning changes.

Grammatically, yes, but it sounds different.

• reinigen = to clean, often more formal or technical
• sauber machen = to clean, very common in everyday speech
• putzen = also often used for cleaning

So:

• Ich reinige den Balkon is correct, but a bit more formal.
• Ich mache den Balkon sauber sounds natural and conversational.
• Ich putze den Balkon may also work, depending on context.

In this sentence, sauber machen is a very natural everyday choice.