Я и так устал, поэтому пойду спать пораньше.

In this sentence, и так means something like already as it is, anyway, or even without anything else happening.

So Я и так устал means:

• I’m already tired
• I’m tired as it is
• I’m tired anyway

It often adds the idea that the situation is already true, so there is no need for anything more.
For example, the speaker is saying: I’m already tired, so I’ll go to bed earlier.

Be careful: и так can have slightly different shades of meaning in other contexts, but already/as it is is the key idea here.

Устал is the short past/result form meaning got tired / am tired in a verbal sense. In everyday Russian, it is the normal way to say I’m tired.

• Я устал = I’m tired
• Я устала = said by a woman

By contrast, усталый is an adjective meaning tired in a more descriptive sense:

• Я усталый sounds less natural in many everyday situations
• усталый человек = a tired person
• у меня усталый вид = I look tired

So for I’m tired, Russian usually prefers Я устал / Я устала.

Пойду is the future form of the perfective verb пойти. Here it means I’ll go.

Russian often uses пойти + infinitive to mean go and do something or start doing something with movement implied.

So:

• пойду спать = I’ll go to bed / I’ll go sleep

Why not the others?

• иду = I’m going right now
• буду идти = I will be going / I’ll be on my way, which does not fit this meaning well

The speaker is making a decision about what they will do next, so пойду is the natural choice.

This is a very common Russian pattern:

• пойти / идти + infinitive

It means to go do something.

Examples:

• пойду есть = I’ll go eat
• пойду работать = I’ll go work
• пойду отдыхать = I’ll go rest
• пойду спать = I’ll go to bed / I’ll go sleep

English usually says go to bed, but Russian often says literally go sleep. That is completely normal.

They are related, but they do different jobs.

• поэтому = therefore / so / that’s why
• потому что = because

In your sentence:

• Я и так устал, поэтому пойду спать пораньше.
• I’m already tired, so I’ll go to bed earlier.

Here the first clause gives the reason, and поэтому introduces the result.

Compare:

• Я пойду спать пораньше, потому что я устал.
  I’ll go to bed earlier because I’m tired.

So:

• поэтому points forward to the consequence
• потому что introduces the cause

Пораньше means earlier or a bit earlier.

It comes from рано (early), but it is comparative in meaning:

• рано = early
• раньше = earlier
• пораньше = a little earlier / somewhat earlier / earlier than usual

So:

• пойду спать рано = I’ll go to bed early
• пойду спать пораньше = I’ll go to bed earlier (than usual / than expected)

The prefix по- often softens the comparison and can make it sound more conversational.

Russian often omits the subject pronoun when it is already clear from the verb form.

Here:

• пойду already means I will go

So Я и так устал, поэтому пойду спать пораньше is perfectly natural.

You could say поэтому я пойду спать пораньше, but it is not necessary. Adding я may give a little extra emphasis or just reflect personal style.

Russian drops pronouns much more freely than English when the meaning is obvious.

In the past tense, Russian verbs show gender in the singular.

So:

• Я устал = said by a man
• Я устала = said by a woman

Everything else in the sentence stays the same:

• Я и так устала, поэтому пойду спать пораньше.

This is very important in Russian: past-tense verb forms often tell you the speaker’s gender.

No, Russian word order is flexible, although some orders sound more natural than others.

The original sentence:

• Я и так устал, поэтому пойду спать пораньше.

is very natural and neutral.

You might also hear:

• Я устал и так, поэтому пойду спать пораньше.
• Поэтому пойду спать пораньше: я и так устал.
• Я и так устал, поэтому я пойду спать пораньше.

But changing word order can slightly change emphasis.

For learners, the original version is a good model:

1. statement of condition/reason
2. поэтому
3. result

Literally, it is closer to go sleep, but in natural English it is often best translated as either:

• go to bed
• go to sleep

Which one fits better depends on context.

In many everyday situations, пойду спать is basically what an English speaker means by I’m going to bed.

If you want to emphasize the act of falling asleep, Russian might use other expressions too, but пойду спать is the standard, natural phrase.

Yes, very often.

Я и так устал can sound like:

• I’m already tired
• I’m tired enough as it is
• I’m tired anyway

Depending on tone, it may suggest that the speaker feels there is already sufficient reason, or that things are already difficult enough.

So the sentence can feel a little more expressive than the plain:

• Я устал, поэтому пойду спать пораньше.

Adding и так gives extra nuance: the tiredness is not just a fact, but something the speaker feels is already true to a significant degree.