Wenn meine Oma zu Besuch kommt, trinken wir zusammen Tee.

Because Wenn meine Oma zu Besuch kommt is a subordinate clause introduced by wenn.

In German, a subordinate clause usually sends the conjugated verb to the end:

• wenn
  • subject + other elements + verb
• Wenn meine Oma zu Besuch kommt

This is one of the most important German word order patterns to learn.

Compare:

• Meine Oma kommt zu Besuch. = normal main clause
• Wenn meine Oma zu Besuch kommt, ... = subordinate clause, so kommt moves to the end

Because the sentence starts with a subordinate clause, and that whole clause takes up position 1 in the main clause.

German main clauses usually put the finite verb in position 2. So after the opening clause, the verb comes immediately:

• Wenn meine Oma zu Besuch kommt, trinken wir zusammen Tee.

Structure:

1. Wenn meine Oma zu Besuch kommt = position 1
2. trinken = position 2
3. wir = then the subject

This is called inversion.

If you put the main clause first, the word order is more like English:

• Wir trinken zusammen Tee, wenn meine Oma zu Besuch kommt.

Here wenn means when or whenever, depending on context.

In sentences like this, wenn is often used for:

• repeated events / habits: whenever
• a future condition: when / if

So this sentence could imply:

• Whenever my grandma comes to visit, we drink tea together.
• When my grandma comes to visit, we drink tea together.

German wenn often covers both ideas where English distinguishes between if and when.

A useful rule:

• wenn = if / whenever / when (for repeated or future situations)
• als = when (for a single event in the past)

Zu Besuch means visiting or on a visit.

So:

• Meine Oma kommt zu Besuch. = My grandma comes to visit.

It is a fixed expression in German. Literally, it looks a bit like to visit, but you should learn it as a chunk:

• zu Besuch kommen = to come visit
• zu Besuch sein = to be visiting

Examples:

• Sie ist bei uns zu Besuch. = She is visiting us.
• Meine Freunde kommen morgen zu Besuch. = My friends are coming to visit tomorrow.

Because meine Oma is the subject of the subordinate clause, so it is in the nominative case.

The verb is kommt, and we ask: Who comes?
Answer: meine Oma

So we need nominative:

• meine Oma = my grandma

You would use meiner Oma in other cases, for example dative:

• Ich helfe meiner Oma. = I help my grandma.

Because the subject is meine Oma, which is third person singular.

So the verb kommen is conjugated as:

• ich komme
• du kommst
• er/sie/es kommt
• wir kommen
• ihr kommt
• sie/Sie kommen

Since Oma = she, the correct form is kommt.

Zusammen means together.

It tells us how we drink tea:

• trinken wir zusammen Tee = we drink tea together

Its placement is natural here, between the subject and the object. German word order is flexible, but this is a very common and natural position.

Compare:

• Wir trinken zusammen Tee.
• Wir trinken Tee zusammen.

Both are possible, but zusammen Tee sounds especially natural in this sentence.

Because all German nouns are capitalized.

So:

• die Oma
• der Besuch
• der Tee

This is true no matter where the noun appears in the sentence.

Examples:

• Ich trinke Wasser.
• Das Buch ist interessant.
• Meine Oma mag Kuchen.

Because in German, a subordinate clause is separated by a comma from the main clause.

So in:

• Wenn meine Oma zu Besuch kommt, trinken wir zusammen Tee.

the comma marks the end of the wenn-clause.

This comma is required in standard German.

Yes. That sentence is grammatically correct.

• Wenn meine Oma kommt, trinken wir zusammen Tee. = When my grandma comes, we drink tea together.

However, zu Besuch kommt is more specific. It clearly means comes to visit.

Without zu Besuch, kommt just means comes, and the exact idea depends more on context.

So:

• kommt = comes
• kommt zu Besuch = comes to visit

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

So:

• Wenn meine Oma zu Besuch kommt can refer to a future event
• trinken wir zusammen Tee can describe what happens then

English sometimes prefers comes in time clauses too:

• When my grandma comes to visit, we drink tea together.

So this works similarly in both languages.

Oma is very common and completely normal in everyday German.

It is warm and familiar, like grandma in English.

Other possibilities include:

• Großmutter = grandmother, more formal or less personal
• Oma = grandma, very common in speech

So meine Oma is natural and idiomatic.

The structure is:

Wenn-clause + main clause

More specifically:

• Wenn = subordinating conjunction
• meine Oma = subject of the subordinate clause
• zu Besuch = expression meaning on a visit / to visit
• kommt = verb at the end of the subordinate clause

Then:

• trinken = finite verb in position 2 of the main clause
• wir = subject
• zusammen = adverb
• Tee = object

So the full pattern is:

Wenn + subject + other elements + verb, verb + subject + ...

That is a very common German sentence pattern.