Перекрутка началась сразу.

It is in the nominative singular.

Why:

• It is the subject of the sentence — the thing that started.
• The ending -а is a very common nominative singular ending for feminine nouns.

So grammatically, перекрутка is the noun that the verb agrees with.

In the past tense, Russian verbs agree with the subject in gender and number.

Here the subject is перекрутка, which is:

• feminine
• singular

So the verb must also be feminine singular:

• masculine: начался
• feminine: началась
• neuter: началось
• plural: начались

That is why you get перекрутка началась, not начался.

Because началась comes from the verb начаться, which means to begin / to start in the sense that something begins.

Compare:

• начать = to start something
• начаться = to begin / to start (for the event itself)

So:

• Я начал фильм. = I started the film.
• Фильм начался. = The film started.

In your sentence, the event itself began, so Russian uses начаться:

• Перекрутка началась сразу.

-сь is just a variant of -ся.

Russian uses:

• -ся after most consonants
• -сь after vowels in many forms

So:

• начался
• началась
• началось
• начались

Here, -сь is part of the verb начаться. It does not literally mean itself in a simple word-for-word way. In many verbs, -ся / -сь helps form a verb with a different meaning or different grammar.

In this case, it makes the verb intransitive:

• начать что-то = to start something
• начаться = to start / begin

Russian aspect matters a lot here.

• началась is perfective
• начиналась is imperfective

началась presents the start as a single completed point in time:

• the beginning happened

That fits very naturally with сразу:

• Перекрутка началась сразу. = the start happened immediately

If you said начиналась, it would sound more like:

• was beginning
• used to begin
• a background or ongoing view of the action

So in a simple statement about when something started, началась is the normal choice.

Because сразу is an adverb.

It means things like:

• immediately
• right away
• at once

Adverbs do not need case endings or prepositions here. It directly modifies the verb:

• началась сразу = started immediately

This is different from a noun phrase like:

• после этого = after that
• в тот момент = at that moment

But сразу works on its own.

Yes. Russian word order is fairly flexible.

The neutral order here is:

• Перекрутка началась сразу.

But you could also say:

• Сразу началась перекрутка.

That version puts more emphasis on сразу.

In general:

• sentence-initial position often gives extra focus or contrast
• the default order is often the least marked and most neutral

So if you are just learning, Перекрутка началась сразу is a good model.

Because Russian has no articles.

So перекрутка can mean, depending on context:

• the ...
• a ...
• just the general idea of the noun

English has to choose:

• The ... started immediately
• A ... started immediately

Russian leaves that to context. That is completely normal.

It is a noun, but it is closely related to a verb stem.

Russian often forms nouns for:

• actions
• processes
• results
• repeated or characteristic events

The noun перекрутка is built in a very typical Russian way and refers to some kind of process/event connected with перекрут-. Exactly how you translate it depends on context, but grammatically it behaves like an ordinary feminine noun:

• singular nominative: перекрутка
• feminine agreement: началась

So even if the exact English meaning changes by context, the grammar of the sentence stays the same.

Often yes, but the tone changes slightly.

• сразу = right away / immediately / at once
• немедленно = immediately, often a bit more formal or stronger

So:

• Перекрутка началась сразу. sounds natural and neutral.
• Перекрутка началась немедленно. is possible, but may sound a little more formal or emphatic depending on context.

For everyday neutral Russian, сразу is extremely common.