Fass die heiße Pfanne bitte nicht an.

The full verb is anfassen, meaning to touch or to handle.

German anfassen is a separable verb:

• an- = separable prefix
• fassen = main verb part

In a main clause or command, the prefix separates and moves to the end:

• anfassen → Fass ... an.

So Fass die heiße Pfanne bitte nicht an. is built from anfassen.

This is the informal singular imperative of anfassen, used when speaking to one person as du.

From fassen, the du imperative is:

• fass!

Because the verb is separable, the prefix moves away:

• fass ... an

You may also see:

• Fasse die heiße Pfanne nicht an.

That extra -e is grammatically possible, but in modern everyday German fass is more common.

In German commands, the subject pronoun is usually left out.

So instead of:

• Du fasst die Pfanne an. = You touch the pan.

the command becomes:

• Fass die Pfanne an! = Touch the pan!

Including du is unusual unless you want special emphasis or contrast.

Pfanne is a feminine noun, so its article is die.

In this sentence, die heiße Pfanne is the direct object, so it is in the accusative case. For feminine singular nouns, the accusative article is still die, so nothing changes there.

The adjective heiß becomes heiße because after a definite article like die, German usually uses the weak adjective ending -e in this form:

• die heiße Pfanne

A helpful comparison:

• der heiße Topf = nominative masculine
• den heißen Topf = accusative masculine

With feminine:

• die heiße Pfanne = nominative feminine
• die heiße Pfanne = accusative feminine

Nicht negates the action, so the sentence means don’t touch.

In sentences with separable verbs, nicht usually comes before the separated prefix:

• Fass ... nicht an.

Also, the object die heiße Pfanne is definite and specific, so it naturally comes before nicht here:

• Fass die heiße Pfanne bitte nicht an.

That word order sounds very natural.

Bitte softens the command. Without it, the sentence can sound more abrupt. With it, the sentence sounds more like a polite warning or request.

Its position is fairly flexible. All of these are possible:

• Bitte fass die heiße Pfanne nicht an.
• Fass bitte die heiße Pfanne nicht an.
• Fass die heiße Pfanne bitte nicht an.

The version in your sentence is completely natural.

The formal Sie version is:

• Fassen Sie die heiße Pfanne bitte nicht an.

For a Sie command, German uses:

• the verb form fassen
• plus Sie

So:

• informal: Fass die heiße Pfanne bitte nicht an.
• formal: Fassen Sie die heiße Pfanne bitte nicht an.

They are similar, but not always identical.

• anfassen is everyday German and often suggests putting your hand on something or handling it.
• berühren is more neutral and often closer to to touch in a general sense.

For a warning about a hot pan, anfassen is especially natural, because the idea is don’t put your hand on it.

Because all German nouns are capitalized.

So:

• die Pfanne
• der Tisch
• das Wasser

That is a normal rule of German spelling, not something special about this sentence.

The adjective is heiß = hot.

When you add the ending -e, it becomes:

• heiß → heiße

The ß stays. So heiße here is simply the inflected form of heiß.

This can look confusing because heiße can also be a verb form of heißen:

• Ich heiße Anna. = My name is Anna.

But in your sentence, heiße is clearly an adjective describing Pfanne.