Я так растерялся, что начал оправдываться вместо того, чтобы спокойно говорить.

Так ... что is a very common Russian pattern meaning so ... that.

In this sentence:

Я так растерялся, что...
= I got so flustered/confused that...

So the structure is:

• так = so
• что = that

A few similar examples:

• Я так устал, что сразу уснул.
  = I was so tired that I fell asleep immediately.

• Он так спешил, что забыл телефон.
  = He was in such a hurry that he forgot his phone.

Растерялся is the past tense, masculine singular form of the verb растеряться.

Russian past tense changes for gender and number:

• растерялся — masculine
• растерялась — feminine
• растерялось — neuter
• растерялись — plural

So:

• Я так растерялся... = a male speaker is talking
• Я так растерялась... = a female speaker is talking

This is because Russian past tense agrees with the subject in gender and number.

Not exactly. Растеряться usually means something like:

• to get flustered
• to lose one’s composure
• to become confused and not know how to react
• to be thrown off

So Я так растерялся is stronger and more situational than simply I was confused.

It often implies that a person suddenly doesn’t know what to do or say.

Compare:

• Я запутался. = I got confused / I got mixed up
• Я растерялся. = I got flustered / I lost my bearings

In this sentence, растерялся fits well because the speaker then starts reacting badly: начал оправдываться.

This is a very common Russian structure:

• начал + infinitive = started to ...

So:

• начал оправдываться = started defending myself / started making excuses

Russian often uses verbs like:

• начать = to begin/start
• стать = to begin, to start doing something
• продолжать = to continue
• перестать = to stop

Examples:

• Он начал говорить. = He started speaking.
• Она перестала смеяться. = She stopped laughing.

In your sentence, this emphasizes the beginning of the reaction: first the speaker got flustered, then began оправдываться.

Оправдываться means:

• to justify oneself
• to make excuses
• to defend oneself verbally

The -ся ending makes it reflexive, and here that reflexive idea is important: the person is trying to justify themselves.

Compare:

• оправдать = to justify someone / excuse someone
• оправдаться / оправдываться = to justify oneself / make excuses

Examples:

• Он оправдывал друга.
  = He was defending/justifying his friend.

• Он оправдывался.
  = He was defending himself / making excuses.

In this sentence, оправдываться suggests the speaker reacted defensively instead of speaking calmly.

Because the sentence focuses on the process or behavior, not on a single completed result.

• начал оправдываться = started making excuses / started defending himself
• This describes the action as something that began and unfolded.

If you used the perfective оправдаться, it would sound more like to manage to justify oneself or to finish doing so, which is not the point here.

After начал, Russian very often uses an imperfective infinitive because it refers to the beginning of an ongoing action:

• начал читать
• начал писать
• начал говорить

So начал оправдываться is the natural choice.

Вместо того, чтобы means instead of when followed by a verb.

In your sentence:

вместо того, чтобы спокойно говорить
= instead of speaking calmly

This whole expression introduces the action that did not happen.

A useful way to learn it is as a fixed pattern:

• вместо того, чтобы + infinitive

Examples:

• Он играл в телефон вместо того, чтобы работать.
  = He was playing on his phone instead of working.

• Вместо того, чтобы спросить, она ушла.
  = Instead of asking, she left.

Even though вместо by itself usually takes the genitive case, in this structure you should treat вместо того, чтобы as a set phrase.

To an English speaker, it often does feel unnecessary, but in Russian this is the standard idiomatic construction.

You can think of it as roughly:

• instead of that, in order to...
• but in real usage it simply means instead of doing...

So learners usually should not try to analyze it too literally at first. Just memorize:

• вместо того, чтобы + infinitive

This is much more natural than trying to build the phrase word by word.

Because говорить is imperfective and refers to the process of speaking, while сказать is perfective and usually refers to saying something specific / producing one completed utterance.

Here the idea is:

• the speaker should have been speaking calmly
• not just said one thing calmly

So:

• спокойно говорить = to speak calmly
• спокойно сказать = to say something calmly

The first fits much better in this context because it contrasts with оправдываться as a style of communication.

Because it modifies the verb говорить, so Russian needs an adverb.

• спокойный = calm (adjective)
• спокойно = calmly (adverb)

Compare:

• спокойный человек = a calm person
• спокойно говорить = to speak calmly

This is the same kind of difference as:

• quick → quickly
• loud → loudly

Although in English some adverbs do not change form, in Russian adjective and adverb forms are clearly different.

Because Russian punctuation strongly marks subordinate clauses.

In this sentence:

Я так растерялся, что начал оправдываться вместо того, чтобы спокойно говорить.

There are two clause boundaries:

1. ..., что начал...
   The part after что is a subordinate clause: so ... that ...

2. ..., чтобы спокойно говорить
   The part after чтобы belongs to the вместо того, чтобы construction.

Russian generally uses commas more consistently than English in these kinds of structures, so punctuation is something worth noticing early.

Yes, Russian word order is fairly flexible, but the original order is the most neutral and natural.

Original:

Я так растерялся, что начал оправдываться вместо того, чтобы спокойно говорить.

Possible variations exist, for example to emphasize a different part, but not every rearrangement sounds equally natural.

For a learner, it is best to keep this order because it clearly presents:

1. the cause/state — Я так растерялся
2. the result — что начал оправдываться
3. the contrast — вместо того, чтобы спокойно говорить

So yes, Russian allows movement, but this version is a very good standard model.

Yes, Russian often drops the subject pronoun when it is clear from context.

So you might hear:

Так растерялся, что начал оправдываться вместо того, чтобы спокойно говорить.

That would still be understandable, especially in conversation, because растерялся already tells you:

• first person
• singular
• masculine

However, keeping Я is completely normal too. It can make the sentence a bit clearer or more explicit.

Not quite.

• извиняться = to apologize
• оправдываться = to justify oneself / make excuses / defend oneself

Sometimes they can overlap in real situations, but the emphasis is different:

• извиняться focuses on saying sorry
• оправдываться focuses on explaining why you are not at fault, or why what happened is understandable

So in this sentence, оправдываться suggests a defensive reaction, not simply a polite apology.