Als Hausmittel trinke ich Tee mit Honig, wenn ich erkältet bin.

Here, als means as in the sense of in the role of or considered as.

• Als Hausmittel = as a home remedy
• It does not mean when here.

So the sentence starts by saying in what sense the speaker drinks the tea: they drink it as a home remedy.

After als, German very often uses a noun without an article when it describes someone's role, function, or category.

• als Hausmittel = as a home remedy
• als Lehrer = as a teacher
• als Kind = as a child

You can sometimes use an article, but without one is very common and natural here.
So als Hausmittel sounds idiomatic.

German often puts a phrase at the beginning of the sentence to emphasize it or set the context.

So:

• Als Hausmittel trinke ich Tee mit Honig... = As a home remedy, I drink tea with honey...

This fronted phrase takes the first position, so the conjugated verb must still stay in second position:

• Als Hausmittel | trinke | ich ...

That is standard German word order.

Because German main clauses usually follow the V2 rule: the conjugated verb must be in the second position.

In this sentence, the first position is occupied by Als Hausmittel, so the verb comes next:

• Als Hausmittel = position 1
• trinke = position 2
• ich follows after that

Compare:

• Ich trinke Tee mit Honig.
• Als Hausmittel trinke ich Tee mit Honig.

Both are correct; the word order changes because a different element comes first.

Tee is in the accusative case because it is the direct object of trinken.

You drink something, and that thing is the direct object:

• ich trinke Tee

With Tee, you do not see a special article here, so the case is understood from the sentence structure rather than from article endings.

Mit always takes the dative case.

So mit Honig means with honey, and Honig is in the dative after mit.

Because there is no article, the noun itself does not visibly change here:

• mit Honig

If there were an article, you would see the dative more clearly:

• mit dem Honig

So the important rule is: mit + dative.

German often leaves out the article with materials, foods, and substances when speaking generally.

So:

• Tee mit Honig = tea with honey
• not necessarily tea with the honey

This is similar to English, where we usually also say tea with honey, not tea with a honey.

Here, wenn means when in the sense of whenever or if/when under a repeated or general condition.

• wenn ich erkältet bin = when I have a cold / when I am sick with a cold

It is used because this is not a one-time past event. It describes what the speaker generally does in that situation.

So the idea is:

• Whenever I’m sick with a cold, I drink tea with honey.

Because als and wenn are used differently for when in German.

• als = for a single event in the past
• wenn = for repeated events, general situations, or future situations

Examples:

• Als ich krank war, trank ich viel Tee.
  = When I was sick (that one time), I drank a lot of tea.
• Wenn ich krank bin, trinke ich Tee.
  = When(ever) I’m sick, I drink tea.

In your sentence, the speaker means a general habit, so wenn is correct.

Because wenn ich erkältet bin is a subordinate clause, and in German subordinate clauses the conjugated verb usually goes to the end.

So:

• wenn introduces the subordinate clause
• ich = subject
• erkältet = predicate adjective
• bin = conjugated verb at the end

This is a very important German pattern:

• ..., wenn ich müde bin
• ..., weil ich keine Zeit habe
• ..., dass er kommt

Yes. Erkältet is functioning as an adjective here.

• ich bin erkältet = I have a cold / I am suffering from a cold

Literally, it is related to erkälten (to catch a cold / to become chilled), but in everyday German erkältet sein is a very common way to say someone has a cold.

So grammatically:

• ich = subject
• bin = form of sein
• erkältet = predicate adjective

That is just the idiomatic German expression.

German can say:

• ich bin erkältet = I have a cold
• ich habe eine Erkältung = I have a cold / a cold illness

Both are possible, but ich bin erkältet is very common and natural in everyday speech.

So even though English uses have, German often uses sein + adjective here.

In German, a subordinate clause introduced by a word like wenn, weil, dass, or obwohl is normally separated by a comma.

So:

• ..., wenn ich erkältet bin.

This comma is required in standard German spelling.

Yes, absolutely.

You can also say:

• Wenn ich erkältet bin, trinke ich als Hausmittel Tee mit Honig.

When the subordinate clause comes first, the main clause still follows the German word order rule: the conjugated verb comes first in the main clause part after the comma.

So you get:

• Wenn ich erkältet bin, trinke ich ...

not

• Wenn ich erkältet bin, ich trinke ...

It is understandable and grammatically correct, but it can sound a little formal or explanatory depending on context.

More everyday alternatives might be:

• Wenn ich erkältet bin, trinke ich Tee mit Honig als Hausmittel.
• Bei einer Erkältung trinke ich Tee mit Honig.
• Ich trinke bei einer Erkältung Tee mit Honig.

Still, Als Hausmittel trinke ich Tee mit Honig... is perfectly good German if you want to emphasize the idea of a home remedy.

Because the sentence has two clauses:

1. Als Hausmittel trinke ich Tee mit Honig
2. wenn ich erkältet bin

Each clause needs its own subject if the subject is stated. German does not normally omit it just because it was used earlier.

So ich appears in both clauses:

• trinke ich
• wenn ich erkältet bin

That is completely normal.