Ich befestige das Namensschild an der Bluse.

Because befestigen is the infinitive, and befestige is the correct present-tense first-person singular form.

Conjugation in the present tense:

• ich befestige
• du befestigst
• er/sie/es befestigt
• wir befestigen
• ihr befestigt
• sie/Sie befestigen

So with ich, you normally use the -e ending: ich befestige.

The basic form is befestigen.

Here, be- is not separable, so it stays attached to the verb in all normal forms:

• Ich befestige das Namensschild.
• Ich habe das Namensschild befestigt.

You do not split it the way you would with a separable verb like anmachen → Ich mache das Licht an.

So it is best to learn befestigen as one complete verb meaning something like to fasten, to attach, or to secure.

Das Namensschild is the direct object, so it is in the accusative case.

However, with a neuter singular noun like das Namensschild, the article is the same in both nominative and accusative:

• nominative: das Namensschild
• accusative: das Namensschild

So the case has changed grammatically, but you cannot see that change in the article here.

Compare that with a masculine noun, where the change is visible:

• nominative: der Ausweis
• accusative: den Ausweis

Because German very often forms nouns by combining smaller nouns into one compound noun.

Here:

• der Name = name
• das Schild = sign, plate, tag

Together they form das Namensschild = name tag / name badge.

The whole compound takes the gender of the last part:

• das Schild → therefore das Namensschild

So when learning German compounds, the final noun is especially important because it usually determines:

• the gender
• the plural pattern
• the general category of meaning

That -s- is a linking element often used in German compounds. It is sometimes called a Fugen-s.

So:

• Name
• Namens-
• Namensschild

It does not usually have a separate meaning by itself. It is just part of how many compounds are formed.

Unfortunately, there is no single simple rule for when German uses this linking -s-, so it is often best to learn compounds as complete words.

This is a very common question, because an is a two-way preposition.

You may have learned:

• accusative for direction/movement
• dative for location

That rule is useful, but with befestigen, German normally uses the pattern:

• etwas an etwas befestigen

where the second part is typically an + dative:

• an der Bluse
• an der Wand
• am Gürtel

So in this sentence, an der Bluse is the standard idiomatic choice.

A good way to learn it is as a set pattern:

• Ich befestige X an + dative

Even though there is an action of attaching, German treats the blouse here as the place/surface where the item is fixed.

Because Bluse is a feminine noun, and after an in this sentence it is in the dative case.

The feminine singular article changes like this:

• nominative: die Bluse
• accusative: die Bluse
• dative: der Bluse
• genitive: der Bluse

So an der Bluse means that Bluse is in the dative.

Here, an means something like:

• on
• to
• attached to

In this sentence, it expresses the thing that the name tag is being attached to:

• das Namensschild = the thing being attached
• an der Bluse = the blouse it is attached to

So although English might say to the blouse or on the blouse, German uses an here.

The sentence as given is the most neutral word order:

• Ich befestige das Namensschild an der Bluse.

But German word order is somewhat flexible, especially if you want to emphasize a certain part.

For example:

• Das Namensschild befestige ich an der Bluse.
• An der Bluse befestige ich das Namensschild.

The important rule is that in a normal main clause, the conjugated verb stays in second position:

• Ich befestige ...
• Das Namensschild befestige ...
• An der Bluse befestige ...

So yes, you can change the order, but befestige must remain the second element in the clause.

It is definitely correct, and it sounds clear and standard. It is a good verb to know.

That said, in everyday speech, Germans might also use more specific or casual verbs depending on how the name tag is attached:

• anstecken = to pin on
• festmachen = to fasten
• anklemmen = to clip on

For example:

• Ich stecke das Namensschild an die Bluse.
• Ich mache das Namensschild an der Bluse fest.

So befestigen is slightly more neutral or formal, while other verbs may sound more conversational or more specific about the method.