Ég les textann hægt, þannig að ég skil hann betur.

Because les is the 1st person singular present tense form of að lesa (to read).

• að lesa = to read
• ég les = I read / I am reading

The form lesa is the infinitive, like English to read, so it cannot be used directly after ég as the main verb here.

A quick comparison:

• Ég les. = I read.
• Mig langar að lesa. = I want to read.

Textann means the text, and it is in the accusative singular because it is the direct object of les.

Here is the pattern:

• texti = a text (nominative singular)
• textann = the text (accusative singular, definite)

In Icelandic, the definite article is usually attached to the end of the noun rather than written as a separate word like English the.

So:

• Ég les texta. = I read a text.
• Ég les textann. = I read the text.

Because texti is a masculine noun in Icelandic, and pronouns must match the noun’s grammatical gender.

So even though English says it, Icelandic uses:

• hann for masculine nouns
• hún for feminine nouns
• það for neuter nouns

Since texti is masculine, the text is referred to as hann.

In this sentence:

• ég skil hann betur = I understand it better

Here, hann refers back to textann.

Yes, historically it is the neuter singular form of the adjective hægur (slow), but in Icelandic that form is very often used adverbially.

So:

• hægur = slow
• hægt = slowly

In this sentence, hægt describes how the reading happens, so it works like an adverb:

• Ég les textann hægt. = I read the text slowly.

This is very common in Icelandic: the neuter singular form of an adjective can function as an adverb.

Þannig að means so that, so, or in such a way that, depending on context.

In this sentence, it introduces the result or purpose:

• Ég les textann hægt, þannig að ég skil hann betur.
• I read the text slowly, so that I understand it better.

It links the two ideas:

1. I read slowly.
2. As a result, I understand better.

It is a very common expression in Icelandic.

Because Icelandic normally requires an explicit subject in a clause.

English sometimes allows omission in certain structures, but Icelandic usually does not. After þannig að, a new clause begins, and that clause needs its own subject:

• þannig að ég skil hann betur

So even though the subject is still I, Icelandic says it again.

Icelandic word order is fairly flexible, but there are still strong normal patterns. In a simple clause like this, the most natural order is:

• subject + verb + object + adverb/comparative
• ég skil hann betur

That is why betur comes at the end here.

A learner should usually treat this as the default pattern:

• ég skil hann = I understand it
• ég skil hann betur = I understand it better

Other word orders may exist for emphasis, but this one is the neutral, standard choice.

Because betur is the comparative adverb meaning better.

Here it modifies the verb skil (understand), not a noun. So we need an adverb, not an adjective.

• vel = well
• betur = better
• best = best

So:

• Ég skil hann vel. = I understand it well.
• Ég skil hann betur. = I understand it better.

By contrast, betra is often an adjective form, as in:

• betra veður = better weather

No. Að skilja means to understand, not to know in the general sense.

So:

• Ég skil textann. = I understand the text.
• Ég veit það. = I know that.
• Ég þekki hann. = I know him.

This is an important distinction:

• vita = know a fact
• þekkja = know a person/place
• skilja = understand

In your sentence, ég skil hann betur means I understand it better, not I know it better.

The comma separates the two clauses:

• Ég les textann hægt
• þannig að ég skil hann betur

It helps show the structure clearly:

• first clause: what you do
• second clause: the result or purpose

In Icelandic, commas are often used to separate clauses like this. Even if punctuation rules can vary a little in real usage, the comma here is completely natural and helpful.

You could say svo að in many contexts, but þannig að is very natural here because it emphasizes the result: I read slowly, so that / with the result that I understand better.

In everyday Icelandic, both þannig að and svo að can introduce a result or purpose clause, but they are not always identical in tone.

For this sentence, þannig að works very well and sounds idiomatic. A learner should simply recognize it as a common connector meaning so that / so.