Моя одногруппница уже сдала зачёт, а я всё ещё готовлюсь.

Because одногруппница is a feminine noun, so the possessive pronoun has to agree with it.

• мой = masculine
• моя = feminine
• моё = neuter
• мои = plural

So:

• мой друг
• моя подруга
• моя одногруппница

Russian adjectives and pronouns usually match the noun in gender, number, and case.

Одногруппница means a female member of the same study group / class group.

It comes from:

• один = one / same
• группа = group

In many Russian-speaking schools and universities, students are often organized into a fixed group, so одногруппник / одногруппница is a very common word.

Compare:

• одногруппник = male classmate/groupmate
• одногруппница = female classmate/groupmate

It is more specific than English classmate, because it often implies belonging to the same official student group.

Сдала is the past tense feminine singular form of the verb сдать.

Russian past tense forms agree with the subject’s gender and number:

• сдал = he handed in / passed
• сдала = she handed in / passed
• сдало = it did
• сдали = they did

Since одногруппница is feminine, the verb becomes сдала.

Because сдать зачёт is a fixed and very common expression meaning to pass a credit test / get a pass.

Here:

• дать by itself usually means to give
• сдать can mean to hand in, to submit, or in academic contexts to pass an exam/test/check

So сдать зачёт is something you should learn as a set phrase.

Similar expressions:

• сдать экзамен = pass an exam
• сдать тест = pass or take/submit a test, depending on context

Зачёт is a specific academic term. In many Russian-speaking educational systems, it is a pass/fail credit assessment, not always a graded exam.

So it is not always exactly the same as an English exam.

Very roughly:

• экзамен = exam, usually graded
• зачёт = pass/fail credit, often based on course requirements, oral questions, or smaller assessment

That is why learners often leave it untranslated in explanations, or translate it approximately depending on context.

Because зачёт is the direct object of сдала, so it is in the accusative case.

For an inanimate masculine noun, the accusative singular is usually the same as the nominative singular.

So:

• nominative: зачёт
• accusative: зачёт

That is why the form does not change.

Compare with an animate masculine noun:

• вижу студента
  not студент

Уже means already.

It shows that the first action has happened by now, possibly earlier than expected or earlier than the speaker’s own progress.

So уже сдала gives the idea:

• she has already passed it
• that stage is completed

It often contrasts naturally with ещё or всё ещё in another clause, just like in this sentence.

А often marks a contrast or comparison between two clauses.

Here the contrast is:

• she has already passed
• I am still preparing

So а works very naturally.

Comparison:

• и = and, simple addition
• но = but, stronger contradiction
• а = and/but, with contrast or topic shift

In this sentence, а sounds very natural because the speaker is comparing two different situations.

Всё ещё means still.

It emphasizes that something is continuing up to the present moment.

So:

• ещё can mean still, yet, or more, depending on context
• всё ещё specifically strengthens the idea of still

Here:

• я всё ещё готовлюсь = I am still preparing

It often sounds more expressive than just я ещё готовлюсь, though both are possible.

Because the verb is готовиться, which is a reflexive verb.

• готовить = to prepare something
• готовиться = to prepare oneself / to get ready / to study for something

So:

• я готовлю ужин = I am cooking/preparing dinner
• я готовлюсь к зачёту = I am preparing for the credit test

The ending -сь is the reflexive marker here.

Because Russian uses the present tense imperfective to describe an action that is currently in progress or ongoing.

So я готовлюсь means:

• I am preparing
• I am getting ready
• I am studying for it

Russian does not have a separate form exactly like English am preparing. The simple present form often covers both:

• I prepare
• I am preparing

Context tells you which meaning is intended.

Because the action is shown as ongoing, not completed.

• готовиться = imperfective, process
• подготовиться = perfective, become fully prepared / finish preparing

Here the speaker is saying that the preparation is still happening, so the imperfective is the correct choice.

Compare:

• Я всё ещё готовлюсь. = I’m still preparing.
• Я уже подготовилась. = I’ve already finished preparing.
  (if the speaker is female)

Russian often omits information that is obvious from context.

Since the previous clause already mentions зачёт, it is understood that:

• я всё ещё готовлюсь
  really means
• я всё ещё готовлюсь к зачёту

Leaving it out sounds natural because the listener already knows what the speaker is preparing for.

It could be omitted in some contexts, because Russian often drops subject pronouns when the verb form makes the subject clear.

But here я is useful because it creates a clear contrast:

• Моя одногруппница ...
• а я ...

That contrast is one of the main points of the sentence, so keeping я sounds natural and expressive.

Because а is joining two separate clauses, each with its own subject and verb:

• Моя одногруппница уже сдала зачёт
• я всё ещё готовлюсь

In Russian, coordinating conjunctions like а, но, and often и usually require a comma when they connect independent clauses.

The main stresses are:

• моя́
• одногру́ппница
• уже́
• сдала́
• зачёт
• всё ещё́
• готовлю́сь

A couple of especially useful notes:

• зачёт has the letter ё, which always carries stress.
• сдала́ is stressed on the last syllable.
• готовлю́сь is stressed on -лю́-.

Stress is very important in Russian, because it is not always predictable.