Am Abend esse ich eine Mandarine, wenn ich noch Hunger habe.

Because German main clauses follow the verb-second (V2) rule.

That means the finite verb must be the second element in the sentence, not necessarily the second word.

• Ich esse am Abend ...
• Am Abend esse ich ...

Both are correct. In your sentence, Am Abend is placed first for emphasis or because it sets the time frame. Once that happens, the verb esse must come next, and ich follows it.

So:

• Am Abend = first element
• esse = second element
• ich = comes after the verb

Am is a contraction of an dem.

• an dem Abend → am Abend

In time expressions, German often uses am with parts of the day:

• am Morgen = in the morning
• am Nachmittag = in the afternoon
• am Abend = in the evening

So am Abend is the normal idiomatic way to say in the evening.

Because wenn introduces a subordinate clause, and in German subordinate clauses, the conjugated verb usually goes to the end.

So:

• ich habe noch Hunger = main clause word order
• wenn ich noch Hunger habe = subordinate clause word order

This is a very important pattern in German:

• weil ich müde bin
• dass er keine Zeit hat
• wenn sie nach Hause kommt

So the final habe is there because of the wenn clause.

Here, wenn can be understood as if or when, depending on context.

In this sentence, it means something like:

• if I’m still hungry
• or when/whenever I’m still hungry

German wenn is often used for:

1. conditions

   • Wenn ich Zeit habe, komme ich.
     = If I have time, I’ll come.

2. repeated situations / whenever

   • Wenn ich müde bin, trinke ich Tee.
     = When/whenever I’m tired, I drink tea.

In your sentence, it sounds like a general habit or recurring situation, so when/if both fit well in English.

Noch here means still.

So:

• Ich habe Hunger. = I’m hungry.
• Ich habe noch Hunger. = I’m still hungry.

It shows that the hunger continues.

In this sentence, wenn ich noch Hunger habe means:

• if I’m still hungry
• if I’m still feeling hungry

So noch adds the idea of continuation.

German often uses the expression Hunger haben, literally to have hunger, where English uses to be hungry.

So:

• Ich habe Hunger. = I am hungry.
• Hast du Hunger? = Are you hungry?

German can also use an adjective:

• Ich bin hungrig. = I am hungry.

But Hunger haben is often more natural in everyday speech.

So in this sentence, wenn ich noch Hunger habe sounds very normal and idiomatic.

Because Hunger haben is a fixed expression.

German often omits the article in certain common noun expressions, especially with things like physical states or needs:

• Hunger haben = to be hungry
• Durst haben = to be thirsty
• Angst haben = to be afraid

So you normally say:

• Ich habe Hunger.
• not usually Ich habe einen Hunger in neutral everyday German

Using an article would change the tone or meaning and often sounds unusual or emphatic.

Because Mandarine is a feminine noun: die Mandarine.

Here it is the direct object of esse, so it is in the accusative case.

For feminine nouns, the article die changes to eine in the indefinite accusative:

• nominative: eine Mandarine
• accusative: eine Mandarine

So the form happens to look the same here.

Compare with a masculine noun:

• der Apfel → ich esse einen Apfel

But with Mandarine, it stays eine.

Because German often uses the present tense to talk about the future, especially when the time is already clear from context.

Here, Am Abend tells you the time, so German does not need a special future form.

• Am Abend esse ich ... = In the evening I eat / I’ll eat ...
• Morgen gehe ich nach Berlin. = Tomorrow I’m going / I will go to Berlin.

German does have a future form with werden, but it is often unnecessary in everyday speech.

Yes, but the meaning changes slightly.

• am Abend = in the evening / on that evening / during the evening
• abends = in the evenings / in the evening as a habit

So:

• Am Abend esse ich eine Mandarine ...
  sounds like a statement about the evening, possibly today or in a general evening context.

• Abends esse ich eine Mandarine ...
  sounds more clearly like a routine: In the evenings, I eat a mandarin ...

Both can work, but abends is often more habit-like.

Yes. German allows that very easily.

You could say:

• Wenn ich noch Hunger habe, esse ich am Abend eine Mandarine.

That is just as correct.

But notice what happens in the main clause after the subordinate clause: the verb still comes first in the main clause part:

• Wenn ich noch Hunger habe, esse ich ...
• not Wenn ich noch Hunger habe, ich esse ...

This is a common learner mistake. After a fronted subordinate clause, the main clause still follows the V2 rule, and the verb comes immediately after the comma.

It means in the evening.

German usually distinguishes:

• am Abend = in the evening
• in der Nacht or nachts = at night

So am Abend refers to the evening period, not late night.

Yes. Inside the subordinate clause, the order is:

• wenn = subordinating conjunction
• ich = subject
• noch = adverb
• Hunger = object/predicate noun in the expression
• habe = verb at the end

A helpful way to remember it is:

subordinator + subject + middle part + verb at the end

So:

• wenn ich noch Hunger habe
• weil er keine Zeit hat
• dass sie heute arbeitet

This end-position of the verb is one of the most important features of German subordinate clauses.