Διορθώνω τα λάθη μου με μολύβι πριν δείξω το τετράδιο στη δασκάλα.

Greek often leaves out the subject pronoun when the verb ending already tells you who the subject is.
Here, Διορθώνω ends in -ω, which shows 1st person singular, so it already means I correct / I am correcting.

You could add εγώ for emphasis:

• Εγώ διορθώνω... = I am the one correcting...

Διορθώνω is:

• present tense
• active voice
• 1st person singular
• from the verb διορθώνω = correct, fix

Because it is a present-tense imperfective form, it can mean:

• I correct
• I am correcting
• sometimes I usually correct

The exact English translation depends on context.

In Greek, possessive expressions usually keep the definite article. So:

• τα λάθη μου = my mistakes
• το βιβλίο μου = my book
• η τσάντα μου = my bag

Word-for-word, it looks like the mistakes my, but that is just how Greek normally expresses possession.

Also, λάθη is the plural of λάθος (mistake).

Here μου means my. It is a weak possessive pronoun placed after the noun:

• τα λάθη μου = my mistakes

The same form μου can also mean to me in other sentences, so its function depends on context.
In this sentence, because it follows a noun, it is clearly possessive.

με means with, and here it shows the instrument used to do the action:

• με μολύβι = with a pencil

There is no article because the pencil is not specific. It just means using pencil as the writing tool.

Compare:

• με μολύβι = with a pencil / in pencil
• με το μολύβι = with the pencil (a specific pencil)

πριν means before. After πριν, Greek commonly uses a subjunctive-type verb form, often without να.

So:

• πριν δείξω = before I show

The form δείξω comes from δείχνω (show) and is the aorist subjunctive form here.

You may also hear πριν να δείξω, but πριν δείξω is very common and correct.

Because Greek is choosing the action as a single complete event:

• πριν δείξω το τετράδιο = before I show the notebook

The aorist form δείξω views the showing as one whole action.
If Greek used the imperfective form, it would suggest something more ongoing, repeated, or habitual, which does not fit as naturally here.

στη is the contracted form of σε + τη:

• σε = to / in / at
• τη δασκάλα = the teacher (feminine, in this structure)

So:

• στη δασκάλα = to the teacher

With δείχνω, Greek uses σε for the person you show something to:

• δείχνω το τετράδιο στη δασκάλα = I show the notebook to the teacher

All the noun phrases here are in the accusative, but for different reasons:

• τα λάθη μου: direct object of διορθώνω
• το τετράδιο: direct object of δείξω
• στη δασκάλα: object of the preposition σε

Modern Greek uses σε + accusative where English often uses to.

δασκάλα specifically means a female teacher. English teacher is gender-neutral, but Greek often makes gender explicit in the noun itself.

Compare:

• η δασκάλα = the female teacher
• ο δάσκαλος = the male teacher

So στη δασκάλα means to the female teacher.

Greek word order is fairly flexible. This sentence sounds natural as written, but other orders are possible if you want different emphasis.

For example:

• Πριν δείξω το τετράδιο στη δασκάλα, διορθώνω τα λάθη μου με μολύβι.

That still means basically the same thing, but it puts the before part first.
Greek relies a lot on articles, endings, and prepositions, so word order is freer than in English.

A rough pronunciation is:

thyo-RTHO-no ta LA-thi mu me mo-LY-vi prin THEE-kso to te-TRA-thyo sti tha-SKA-la

A few helpful sounds:

• θ sounds like th in think
• δ sounds like th in this
• χ is a harsher sound, like the ch in German Bach or Scottish loch
• γγ / γκ / γχ rules do not matter here, but single γ changes sound depending on what follows

The stressed syllables are marked by the accent marks:

• Διορθώνω
• λάθη
• μολύβι
• δείξω
• τετράδιο
• δασκάλα