Außer Kaffee trinke ich auch Tee.

Here außer means apart from / besides.

So Außer Kaffee trinke ich auch Tee means something like:

• Besides coffee, I also drink tea.
• Apart from coffee, I drink tea too.

In other contexts, außer can also mean except for, so learners often notice that it has more than one possible English translation. In this sentence, the presence of auch makes the additive meaning clear: coffee is included, and tea is added.

Because German main clauses usually follow the verb-second rule.

The sentence begins with Außer Kaffee, which counts as the first element. That means the conjugated verb must come next:

• Außer Kaffee
  • trinke
    • ich
      • auch Tee

If you start instead with ich, then the verb still has to be second:

• Ich trinke außer Kaffee auch Tee.

Both are correct. The version with Außer Kaffee at the front gives that part more emphasis.

Außer normally takes the dative case.

So grammatically, Kaffee is in the dative here. You just cannot see it from the form, because Kaffee without an article looks the same.

You can see the dative more clearly with an article:

• außer dem Kaffee

That said, in your sentence, using no article is completely normal.

Because Kaffee and Tee are being used as general mass nouns.

German often omits the article with food and drink when speaking generally:

• Ich trinke Kaffee.
• Ich trinke Tee.

So here:

• Außer Kaffee trinke ich auch Tee.

means coffee and tea in general, not a specific coffee or a specific tea.

If you added an article, the meaning would become more specific:

• Außer dem Kaffee trinke ich auch den Tee.

That sounds like you are talking about particular drinks in a particular situation, not drinks in general.

Auch means also / too.

It shows that Tee is being added to Kaffee. In other words, the speaker drinks coffee, and tea as well.

Its position matters. Here:

• auch Tee

means tea too.

So the sentence is structured as:

• Apart from coffee, I also drink tea.

If auch moved, the emphasis could shift.

Yes. That is also correct and very natural.

Compare:

• Außer Kaffee trinke ich auch Tee.
• Ich trinke außer Kaffee auch Tee.

The meaning is basically the same. The difference is mainly focus:

• Außer Kaffee... puts more emphasis on coffee as the starting point.
• Ich trinke... is a more neutral statement.

Yes, that is a very common point of confusion.

Außer can mean either:

• except for
• besides / apart from

Context decides which meaning is intended.

In your sentence, auch strongly points to the meaning besides / apart from:

• Außer Kaffee trinke ich auch Tee
  = coffee is one thing I drink, and tea is another.

If the sentence were different, außer could mean except:

• Ich trinke nichts außer Wasser.
  = I drink nothing except water.

So the word itself can go both ways, but this sentence is clearly additive.

Not in the same way.

Außer is a preposition here, and it directly connects to a noun:

• außer Kaffee

Außerdem is an adverb meaning besides / furthermore / in addition. It does not take a noun directly.

So these are different:

• Außer Kaffee trinke ich auch Tee.
• Außerdem trinke ich Tee.

The second one means more like Besides that / Furthermore, I drink tea, but it does not specifically mean besides coffee unless the context already made that clear.

Because in German, all nouns are capitalized.

So:

• Kaffee
• Tee

must both begin with a capital letter.

This is one of the most noticeable spelling differences between German and English.

No.

Außer Kaffee is simply the first element of the sentence, and no comma is needed:

• Außer Kaffee trinke ich auch Tee.

A comma would be wrong here.

Yes, it is natural and correct.

A native speaker might also say:

• Ich trinke außer Kaffee auch Tee.
• Neben Kaffee trinke ich auch Tee.

But your sentence is perfectly good German. It sounds a little more deliberate because Außer Kaffee is placed first for emphasis, but it is still natural.