Auf meiner Bluse ist ein kleiner Fleck, den ich sofort mit Wasser auswasche.

Auf meiner Bluse means on my blouse.

German often begins a sentence with the place or setting if that is what the speaker wants to focus on first. This is completely normal. The basic idea is:

• Auf meiner Bluse ist ein kleiner Fleck.
• literally: On my blouse is a small stain.
• natural English: There is a small stain on my blouse.

So the sentence starts with the location, not the stain itself.

Because auf here is followed by the dative case.

In this sentence, auf describes a location, not movement:

• auf meiner Bluse = on my blouse
• no movement onto the blouse is happening

When auf describes location, it takes the dative. That is why:

• meine Bluse becomes meiner Bluse

This is part of the group of German two-way prepositions. With them:

• location → dative
• movement toward a destination → accusative

Compare:

• Der Fleck ist auf meiner Bluse. = location
• Ich lege die Brosche auf meine Bluse. = movement onto the blouse

Because Fleck is:

• masculine: der Fleck
• here it is the subject of ist
• so it is in the nominative case

With the indefinite article ein in the masculine nominative, the adjective takes -er:

• ein kleiner Fleck

So:

• ein = masculine nominative indefinite article
• kleiner = adjective ending for that pattern
• Fleck = noun

Den is a relative pronoun. It refers back to ein kleiner Fleck.

So this part:

• den ich sofort mit Wasser auswasche

means:

• which I wash out immediately with water

Since Fleck is masculine singular, the relative pronoun has to match it in gender and number.

But the case of the relative pronoun is decided by its role inside the relative clause, not by the earlier noun.

Here, inside the clause:

• ich wasche den Fleck aus

The stain is the direct object, so it must be in the accusative.

That is why we get:

• der Fleck in the main clause
• den in the relative clause

Because that part is a relative clause, and German always separates relative clauses with commas.

So:

• Auf meiner Bluse ist ein kleiner Fleck, den ich sofort mit Wasser auswasche.

The comma shows that den ich sofort mit Wasser auswasche adds extra information about ein kleiner Fleck.

This is much stricter in German than in English. In German, the comma is required.

Because den ich sofort mit Wasser auswasche is a subordinate clause—more specifically, a relative clause.

In German subordinate clauses, the conjugated verb normally goes to the end.

Compare:

• main clause: Ich wasche den Fleck sofort mit Wasser aus.
• relative clause: ..., den ich sofort mit Wasser auswasche.

So the verb moves to the end because of the clause type.

Because auswaschen is a separable verb.

Its base form is:

• auswaschen = to wash out

In a normal main clause, separable verbs split:

• Ich wasche den Fleck aus.

In a subordinate clause, they do not split:

• ..., den ich auswasche.

So:

• main clause → wasche ... aus
• subordinate clause → auswasche

That is exactly what happens here.

Auswaschen means to wash out, especially removing something from fabric or another material using water or washing.

Here it means removing the stain from the blouse.

It is a good verb for things like:

• stains
• dirt
• color
• residue

In this sentence, mit Wasser auswaschen suggests washing the stain out using water.

Because German often leaves out the article when talking about a material or substance in a general way.

So:

• mit Wasser = with water
• not a specific water, just water as a substance

This is similar to English, where we also usually say with water, not with the water, unless we mean a specific water already mentioned.

Also, mit always takes the dative, and Wasser is a neuter noun. But because there is no article here, you just see:

• mit Wasser

Yes, it is in the present tense:

• ist
• auswasche

German very often uses the present tense for actions happening:

• now
• very soon
• as a general habit
• as part of a narration

So den ich sofort mit Wasser auswasche can mean something like:

• which I immediately wash out with water
• or more naturally in English, which I’m going to wash out right away with water

German does not need a special future form here.

Sofort means immediately or right away.

It tells you when the speaker washes out the stain.

In the relative clause:

• den ich sofort mit Wasser auswasche

the word order is natural and clear:

• den = object
• ich = subject
• sofort = time adverb
• mit Wasser = means/method
• auswasche = verb at the end

You could sometimes move adverbs around in German, but this position is very normal.

Yes. That would be a natural follow-up sentence if the stain has already been mentioned.

For example:

• Auf meiner Bluse ist ein kleiner Fleck. Ich wasche ihn sofort mit Wasser aus.

Here:

• ihn refers to den Fleck
• ihn is masculine accusative singular

The version in your original sentence uses a relative clause to combine both ideas into one sentence.

Because German often uses sein to say that something is somewhere:

• Auf meiner Bluse ist ein kleiner Fleck.

This is the normal way to say There is a small stain on my blouse.

You could sometimes use es gibt, but it is not the best choice here. Es gibt usually means there is/there are in a more general sense, not specifically located on something in this way.

So for physical location, ist is more natural here.

Yes. Fleck can mean:

• spot
• stain
• mark
• sometimes even patch or small area

In this sentence, because it is on a blouse and being washed out with water, stain is clearly the best meaning.

The context tells you which English word fits best.