Bitte lies den Satz noch einmal und achte auf jedes Komma.

Lies is the informal singular imperative of lesen, used when speaking to one person you would call du.

• lesen = infinitive, to read
• du liest = you read
• lies! = read!

The verb lesen changes its stem vowel from e to ie in some forms, including du liest and the imperative lies.

So Bitte lies den Satz ... means Please read the sentence ... when talking to one person informally.

In German, the imperative usually leaves out the subject pronoun.

So instead of saying:

• Du lies den Satz ... — which is not how commands are normally formed

German says:

• Lies den Satz ...

The du is understood. English can do something similar: Read the sentence again. You do not need to say You read the sentence again.

Here bitte means please. It makes the command sound more polite.

You can often place bitte in different positions:

• Bitte lies den Satz noch einmal.
• Lies bitte den Satz noch einmal.

Both are natural. In your sentence, bitte comes first, which is very common.

Because lesen takes a direct object, and direct objects are usually in the accusative case.

The noun Satz is masculine: der Satz

So in the accusative it becomes:

• der Satz → den Satz

That is why the sentence says lies den Satz.

Noch einmal means once again, one more time, or again.

In this sentence, noch einmal emphasizes repeating the action:

• lies den Satz noch einmal = read the sentence one more time

You may also see wieder, which often also means again. In many contexts, wieder and noch einmal are close in meaning, but noch einmal often more clearly suggests one additional time.

So here noch einmal is very natural because the speaker wants the person to read it another time carefully.

Because achten auf is a fixed verb + preposition combination meaning to pay attention to or to watch for.

So:

• auf etwas achten = to pay attention to something

In the sentence:

• achte auf jedes Komma = pay attention to every comma

This is not a separable-prefix verb. It is the verb achten used with the preposition auf.

Because Komma is a neuter noun:

• das Komma

After auf, this phrase is in the accusative because achten auf takes the accusative.

For a neuter singular noun, jed- takes the form jedes in the accusative:

• jedes Komma = every comma

Compare:

• jeder Satz = every sentence masculine nominative
• jeden Satz = every sentence masculine accusative
• jedes Komma = every comma neuter nominative/accusative

In German, all nouns are capitalized, not just names or sentence-initial words.

So:

• der Satz
• das Komma

are capitalized because they are nouns.

This is one of the most noticeable spelling differences between German and English.

Because the two commands are simply joined by und:

• Bitte lies den Satz noch einmal
• und achte auf jedes Komma

In German, when two main clauses are connected by und, you usually do not need a comma.

So the sentence is correctly written without one.

That is typical of the imperative in German.

In commands, the verb usually comes first:

• Lies den Satz ...
• Achte auf jedes Komma.

When two commands are linked with und, each command keeps that imperative structure. So after und, you again get the verb early:

• ... und achte auf jedes Komma

German has different imperative forms depending on who you are addressing.

• Informal singular one person, du:

  • Bitte lies den Satz noch einmal und achte auf jedes Komma.

• Informal plural more than one person, ihr:

  • Bitte lest den Satz noch einmal und achtet auf jedes Komma.

• Formal one or more people, Sie:

  • Bitte lesen Sie den Satz noch einmal und achten Sie auf jedes Komma.

So your original sentence is specifically addressed to one person informally.