Meine Freundin markiert wichtige Sätze mit dem Textmarker, damit sie sie vor der Prüfung schneller findet.

Because Freundin is a feminine noun, so the possessive word has to match that gender in the nominative singular:

• mein Freund = my male friend / boyfriend
• meine Freundin = my female friend / girlfriend

Here, meine Freundin is the subject of the sentence, so it is in the nominative case.

It can mean either, depending on context.

• meine Freundin can mean my girlfriend
• but it can also mean my female friend

German often relies on context here. If someone wants to make it completely clear they mean just a friend, they might say:

• eine Freundin von mir = a female friend of mine

Because wichtige Sätze is in the accusative plural after the verb markieren.

The noun is:

• der Satz = sentence
• plural: die Sätze

After markieren, the thing being marked is the direct object, so we need accusative plural. With no article in front, the adjective takes the ending -e in the plural here:

• wichtige Sätze = important sentences

So:

• Meine Freundin markiert wichtige Sätze.

is correct.

Because der Satz is one of many German nouns that change their vowel in the plural:

• singular: der Satz
• plural: die Sätze

This kind of vowel change is very common in German, especially with short, common nouns.

Because mit always takes the dative case.

The noun is:

• der Textmarker = the highlighter

In the dative singular, der becomes dem:

• mit dem Textmarker = with the highlighter

So the pattern is:

• mit + dative

Examples:

• mit dem Stift
• mit der Hand
• mit den Freunden

Der Textmarker is the German word for a highlighter.

It is a compound noun:

• Text = text
• Marker = marker

So literally it is something like text marker, but in natural English the meaning is highlighter.

Because damit introduces a subordinate clause, and in German subordinate clauses are normally separated from the main clause by a comma.

Main clause:

• Meine Freundin markiert wichtige Sätze mit dem Textmarker

Subordinate clause:

• damit sie sie vor der Prüfung schneller findet

So the comma is required.

Here damit means so that or in order that. It introduces a clause of purpose.

So the idea is:

• She marks important sentences with a highlighter so that she can find them more quickly before the exam.

This is different from weil, which means because and gives a reason, not a purpose.

Compare:

• ..., damit sie sie schneller findet.
  = ... so that she can find them more quickly.

• ..., weil sie sie schneller finden will.
  = ... because she wants to find them more quickly.

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

Main clause word order:

• Meine Freundin markiert ...

Subordinate clause:

• damit sie sie vor der Prüfung schneller findet

So findet goes to the end because of the subordinate clause structure.

They do two different jobs:

• the first sie = she → the subject
• the second sie = them → the direct object, referring to wichtige Sätze

So:

• damit sie sie ... findet
• so that she finds them ...

German uses the same written form sie for several meanings, including:

• she
• they
• them
• you (formal, capitalized: Sie)

You understand the meaning from context and grammar.

Because wichtige Sätze is plural, and the accusative plural pronoun for them is sie.

So the sentence goes like this:

• wichtige Sätze = important sentences
• later replaced by sie = them

That avoids repeating the noun:

• ..., damit sie wichtige Sätze vor der Prüfung schneller findet
• ..., damit sie sie vor der Prüfung schneller findet

Both are possible, but the version with sie sounds more natural because it avoids repetition.

Because German usually forms the comparative of adverbs and adjectives by adding -er.

• schnell = fast / quickly
• schneller = faster / more quickly

Here schneller works adverbially, describing how she finds them:

• sie findet sie schneller = she finds them more quickly

German does not normally say mehr schnell for this.

Because vor can take either the accusative or the dative, depending on meaning.

Here it is used in a temporal sense:

• vor der Prüfung = before the exam

Temporal vor takes the dative, so:

• die Prüfung → der Prüfung in the dative singular

Compare:

• vor der Prüfung = before the exam
• vor dem Haus = in front of the house

German often expresses this kind of idea without using a separate modal verb like kann.

The clause:

• damit sie sie vor der Prüfung schneller findet

literally means:

• so that she finds them more quickly before the exam

But in natural English, we often translate this as:

• so that she can find them more quickly before the exam

That can is often implied by the purpose structure in English, even though it is not explicitly stated in German.

Yes, but only if the subject of both parts is the same.

Here the subject of the main clause is meine Freundin, and the subject of the purpose clause is also sie referring to the same person. So you could say:

• Meine Freundin markiert wichtige Sätze mit dem Textmarker, um sie vor der Prüfung schneller zu finden.

That means the same thing.

A useful difference:

• um ... zu is used when the subject is the same
• damit can be used more generally, including when the subjects are different

Yes. The main clause follows normal German word order:

• Meine Freundin = subject
• markiert = verb in second position
• wichtige Sätze = object
• mit dem Textmarker = prepositional phrase

So the main clause is:

• Meine Freundin markiert wichtige Sätze mit dem Textmarker

This is a very standard structure: subject + verb + object + additional information.

Yes. German word order is flexible, especially with adverbial or prepositional phrases.

For example, you could also say:

• Meine Freundin markiert mit dem Textmarker wichtige Sätze, damit sie sie vor der Prüfung schneller findet.

That is also correct.

The original version sounds very natural, but German often allows this kind of movement as long as the sentence remains clear.

Because all nouns are capitalized in German.

So in this sentence, the nouns are:

• Freundin
• Sätze
• Textmarker
• Prüfung

This is one of the most noticeable spelling rules in German.