Meine Enkelin findet im Garten eine grüne Murmel.

Because Enkelin is a feminine noun.

The possessive mein- changes its ending to match the gender, number, and case of the noun:

• mein Enkel = my grandson
• meine Enkelin = my granddaughter

Here, Enkelin is feminine singular nominative because it is the subject of the sentence, so meine is the correct form.

The ending -in is a very common way to form a female person noun in German.

For example:

• der Enkel = grandson
• die Enkelin = granddaughter

You will see this pattern a lot:

• der Lehrer → die Lehrerin
• der Freund → die Freundin

So Enkelin specifically means a female grandchild.

Because the subject is Meine Enkelin, which is third person singular: she finds.

The verb finden is the infinitive, meaning to find. In the present tense, it changes like this:

• ich finde
• du findest
• er/sie/es findet
• wir finden
• ihr findet
• sie/Sie finden

So with meine Enkelin, you need findet.

It is in the accusative case because it is the direct object of findet.

Ask: What does my granddaughter find?
Answer: eine grüne Murmel

That makes eine grüne Murmel the thing being found, so it is the direct object.

In this sentence:

• Meine Enkelin = nominative subject
• eine grüne Murmel = accusative object

Because Murmel is feminine, and the phrase is in the accusative singular.

The article and adjective must agree with the noun:

• eine = feminine singular indefinite article
• grüne = adjective ending used after eine with a feminine singular noun
• Murmel = feminine noun

So:

• eine Murmel = a marble
• eine grüne Murmel = a green marble

For feminine singular, the adjective ending here is -e.

Im is just the contraction of in dem.

• in dem → im

This is very common in German and sounds natural in everyday language.

So these mean the same thing:

• im Garten
• in dem Garten

Usually, im Garten is what people would actually say.

Because this sentence describes location, not movement into somewhere.

German uses in with two different cases:

• dative for location: in the garden
• accusative for direction/movement into: into the garden

Here, the granddaughter finds something while in the garden, so it is a fixed location:

• im Garten = in the garden → dative

If there were movement into the garden, you would use accusative:

• Sie geht in den Garten. = She goes into the garden.

In modern German, many masculine and neuter nouns do not visibly change in the singular dative, especially in everyday language.

What shows the dative here is mainly the article:

• dem Garten
• contracted: im Garten

An older or more formal dative -e sometimes exists, such as im Gartene, but that is archaic and not normal modern usage.

So Garten staying the same is completely normal.

Yes, that is also correct.

German word order is more flexible than English, especially with adverbial phrases like im Garten.

Both are grammatical:

• Meine Enkelin findet im Garten eine grüne Murmel.
• Meine Enkelin findet eine grüne Murmel im Garten.

The difference is mostly one of focus or rhythm:

• findet im Garten eine grüne Murmel can highlight where the finding happens a bit earlier
• findet eine grüne Murmel im Garten presents the object first after the verb, which may feel more straightforward to an English speaker

Both are natural.

Because all nouns are capitalized in German.

That is a standard spelling rule, not something special about this sentence.

So here:

• Enkelin = noun
• Garten = noun
• Murmel = noun

But words like meine, findet, im, and grüne are not nouns, so they are not capitalized.

Here, Murmel means a marble, the small glass ball used as a toy.

It is a feminine noun:

• die Murmel

In other contexts, German has words that look similar, but in this sentence Murmel clearly refers to the object being found in the garden.

The tricky part is the ü.

A rough guide:

• grü- sounds a bit like saying gree but with rounded lips
• -ne is a weak ending, like nuh or a very light neh

So grüne is approximately GRYOO-nuh, but that is only an approximation.

A few pronunciation notes:

• g is a hard g
• r may sound different depending on accent
• ü is not the same as English oo or ee
• the final e in grüne is pronounced lightly, not silent

If you want, I can also break the whole sentence down word by word for pronunciation.