Learn Hardcore Russian: Перед ужином я почистил морковь и нарезал её для супа. - Before dinner I peeled the carrot and sliced it for soup.

Перед requires the instrumental case when it means before / in front of.
So ужин → ужином (instrumental singular).
Pattern: перед + Instrumental (перед домом, перед работой, перед ужином).

Does перед ужином mean “before dinner (in time)” or “in front of dinner (physically)”?

In this context it means before dinner (time).
Russian uses the same preposition перед for both meanings; the context (talking about cooking) makes it clearly temporal.

Why is the verb почистил in the past masculine form?

Past-tense verbs in Russian agree in gender and number with the subject.
Я doesn’t show gender by itself, but the speaker chooses the form:

почистил = “I (male speaker) cleaned/peeled”
почистила = “I (female speaker) cleaned/peeled” Plural would be почистили.

What aspect are почистил and нарезал? What does that imply?

Both are perfective here: they present the actions as completed (a finished result).

почистил = finished peeling/cleaning the carrot
нарезал = finished cutting it (into pieces)

Imperfective would sound like focusing on process/habit:

чистил / резал = “was cleaning / was cutting” or “used to…”

Is нарезал definitely perfective? I thought perfective of резать is разрезать.

Нарезать can function as a perfective meaning “to cut (something) up / slice (a quantity)”, especially when it implies a resulting set of pieces.
So in cooking contexts нарезал морковь commonly means “(I) chopped/sliced the carrot (completely).”
There is also imperfective нарезать in some uses (context-dependent), but here the pairing with почистил and the completed cooking prep strongly pushes the perfective reading.

Why is it морковь and not some different ending for “carrot”? What case is морковь?

It’s the direct object of почистил, so it’s accusative.
For many feminine nouns like морковь (ending in a soft sign -ь), nominative and accusative look the same:

Nom.: морковь
Acc.: морковь
So the form doesn’t change even though the case does.

What does почистил морковь mean exactly—“cleaned” or “peeled”?

In food contexts, почистить often means to peel (remove the skin) or to clean/prepare the item.
So почистил морковь is most naturally “peeled the carrot” (or “cleaned the carrot,” depending on context, but peeling is common).

Why is её used? Could you omit it?

Её means “it / her” and refers back to морковь. It’s used because the second verb (нарезал) still needs an object: “cut it.”
You can omit it if it’s obvious from context:

…я почистил морковь и нарезал для супа.
But including её sounds clearer and more natural, especially in writing.

Why is it её and not её with a different ending? What case is её?

Её is the accusative (and also genitive) form of the 3rd person feminine pronoun (она).
Here it’s accusative because it’s the direct object of нарезал.
Note: её is indeclinable in spelling (it doesn’t change form here), unlike many adjectives/nouns.

Where should the stress go in её and how is it pronounced?

Её is stressed on the second syllable: е-Ё.
Common pronunciation: roughly [yeyo] (with ё sounding like yo).
In writing, ё is sometimes replaced by е, but её is usually written with ё because it prevents confusion.

Why is it для супа and not для суп? What case is супа?

Для requires the genitive case (“for (the purpose of)”).
So суп → супа (genitive singular).
Pattern: для + Genitive (для работы, для друга, для супа).

Could the word order be different? For example, Я перед ужином… or …для супа её?

Yes—Russian word order is flexible, but it changes emphasis.

Перед ужином я… emphasizes the time frame (“Before dinner, I…”).
Я перед ужином… emphasizes the subject (“I, before dinner…”).
…нарезал её для супа is neutral.
…нарезал для супа её is possible but more marked; it highlights её (“cut it for the soup”).

Why is there no comma before и?

Because и connects two verbs (почистил and нарезал) that share the same subject (я) and form a simple compound predicate. In that structure, Russian normally does not use a comma:

я почистил … и нарезал …
A comma would appear if the sentence were more complex (e.g., separate clauses with different subjects, or inserted phrases).