Я насыпала муку в большую миску и начала делать блины.

It means something like poured in, put in, or added a loose substance.

Russian uses насыпать for things like flour, sugar, salt, grain, sand, and other dry particles. So насыпала муку sounds more natural than a more general verb like положила.

Because the verb in the past tense shows the speaker’s gender.

With Я:

• я насыпал = a male speaker
• я насыпала = a female speaker

The same is true for начала:

• я начал = male
• я начала = female

So this sentence is being said by a woman.

Because it is the direct object of the verb, so it goes into the accusative case.

Мука is a feminine noun ending in -а, and in the singular accusative that ending usually changes to -у:

• мука → nominative
• муку → accusative

So насыпала муку means poured in flour.

Because в can take different cases depending on the meaning:

• в + accusative = movement into
• в + prepositional = location in

Here the flour is being poured into the bowl, so Russian uses the accusative:

• в большую миску = into a big bowl

If you were just describing where something already is, you would say:

• в большой миске = in a big bowl

Because the adjective has to agree with миска in gender, number, and case.

Here миску is:

• feminine
• singular
• accusative

So the adjective must also be feminine singular accusative:

• большая миска = nominative
• в большую миску = accusative

After начать in Russian, the following infinitive is usually imperfective, because it names the activity that is starting.

So:

• начала делать блины = started making pancakes

This is natural because делать focuses on the process or activity.

Using сделать after начать is much less natural here, because сделать focuses on completion, not the ongoing action.

Yes, absolutely.

In fact, печь блины is very common and often sounds even more idiomatic when talking about cooking them.

The difference is roughly:

• делать блины = make pancakes, in a broad sense
• печь блины = cook/bake/fry pancakes, focusing more on the actual preparation

So this sentence is fine, but начала печь блины would also be very natural in many contexts.

Because people usually make pancakes in batches, not just one.

So Russian naturally says:

• делать блины = make pancakes

If you wanted to talk about one pancake, you would use the singular:

• блин

But in everyday cooking contexts, the plural is much more common.

The sentence mixes a completed action with the start of an ongoing activity:

• насыпала is understood here as a completed action: she poured the flour into the bowl
• начала is also a completed starting event: she started
• делать is imperfective: it describes the activity she began

So the overall structure is very typical Russian:

1. one finished action
2. then the beginning of a process

Yes. Russian often leaves out subject pronouns when the meaning is clear from context.

So this would also be natural:

Насыпала муку в большую миску и начала делать блины.

The verb endings already show it is I and that the speaker is female.

Including Я can make the sentence a little more explicit or slightly more contrastive, but it is not required.

Because Russian has no articles.

So Russian simply says:

• муку
• в большую миску
• делать блины

English has to choose between a, the, or no article, but Russian leaves that to context.

A natural stressed version is:

Я насы́пала муку́ в большу́ю ми́ску и начала́ де́лать блины́.

A useful thing to notice is that начала́ has final stress here, because it is from начать meaning to begin/start.