Kannst du bitte den Zettel an die Pinnwand anstecken?

Because anstecken is a separable verb.

• The full infinitive is anstecken.
• In a main clause, the prefix an- separates from the verb.
• The conjugated part goes to the usual verb position, and the prefix goes to the end.

So:

• du steckst ... an = you attach ...
• Kannst du ... anstecken? = Can you attach ... ?

With a modal verb like kannst, the full infinitive anstecken stays at the end.

This is the normal word order for a yes/no question in German.

In a statement, you would say:

• Du kannst bitte den Zettel an die Pinnwand anstecken.
  This sounds less natural as a request, though.

In a question, the conjugated verb comes first:

• Kannst du bitte den Zettel an die Pinnwand anstecken?

Even though it literally means Can you ...?, it is often used as a polite request, just like in English.

Because Zettel is the direct object of the sentence, so it is in the accusative case.

The noun is masculine:

• nominative: der Zettel
• accusative: den Zettel

Here, the thing being attached is the note, so German uses the accusative:

• den Zettel anstecken = attach the note

Because an is a preposition that can take either the dative or the accusative, depending on meaning.

Here it expresses direction or movement toward a surface: the note is being attached onto/to the notice board. That is why German uses the accusative:

• an die Pinnwand

Since Pinnwand is feminine:

• nominative: die Pinnwand
• accusative: die Pinnwand

So the article looks the same, but the case is still accusative.

German often uses an when something is attached to a vertical surface or placed against it.

A Pinnwand is like a board on a wall, so an die Pinnwand is natural: onto / to the notice board.

Very roughly:

• an = to / onto / on a vertical surface
• auf = on top of a horizontal surface

So for a board on the wall, an die Pinnwand is the usual choice.

Zettel usually means a note, slip of paper, or small piece of paper.

Depending on context, it could be:

• a note
• a memo
• a little paper notice
• a scrap of paper

In this sentence, note is probably the most natural translation.

Pinnwand means a notice board, pinboard, or bulletin board.

It is made from:

• Pinn- related to pinnen / pins
• Wand = wall

So it is literally something like a pin-wall, but in natural English you would usually say notice board or pinboard.

No. Anstecken has several meanings.

Common ones include:

• to attach / pin up / fasten
• to plug in
• to infect or pass something on in the sense of illness

So context matters.

Examples:

• den Zettel anstecken = attach the note
• das Kabel anstecken = plug in the cable
• jemanden anstecken = infect someone

That is a very common source of confusion for learners.

Bitte makes the request more polite, like please in English.

Its position is flexible, but this placement is very common:

• Kannst du bitte den Zettel an die Pinnwand anstecken?

You could also hear:

• Kannst du den Zettel bitte an die Pinnwand anstecken?

Both are natural. German often allows bitte to move around a little without changing the meaning much.

Kannst du bitte ... ? is perfectly normal and polite in everyday speech, especially with du.

But German can sound softer or more formal with forms like:

• Kannst du bitte ... ? = normal, polite
• Könntest du bitte ... ? = a bit softer, more tentative
• Kannst du mal bitte ... ? = often very natural in conversation
• Können Sie bitte ... ? = polite/formal with Sie

So the sentence is polite, but not extremely formal.

Du is the informal way to say you in German.

Use du with:

• friends
• family
• children
• classmates
• coworkers in informal workplaces

Use Sie in more formal situations or with people you do not know well.

So the formal version would be:

• Können Sie bitte den Zettel an die Pinnwand anstecken?

or a slightly softer version:

• Könnten Sie bitte den Zettel an die Pinnwand anstecken?

No, that would change the grammar and sound wrong in this context.

• an die Pinnwand uses the accusative and shows movement/direction: attaching the note to the board
• an der Pinnwand uses the dative and would describe a location: at the notice board

So here you need:

• an die Pinnwand anstecken

because the note is being moved and attached there.

Because in German, all nouns are capitalized.

So:

• der Zettel
• die Pinnwand

This is a standard rule in German spelling and is one of the easiest ways to spot nouns in a sentence.