Η ανακοίνωση λέει ότι η επιβίβαση αρχίζει σε δέκα λεπτά.

It means the announcement.

• η = the for a feminine singular noun
• ανακοίνωση = announcement

Ανακοίνωση is a very common word for a public announcement, such as at an airport, station, or on a loudspeaker.

λέει is the third-person singular present form of λέω, meaning to say.

So:

• η ανακοίνωση λέει = the announcement says

Greek uses the present tense here just like English does.

ότι means that and introduces a new clause:

• Η ανακοίνωση λέει ότι...
• The announcement says that...

In English, that is often optional, but in Greek it is very commonly kept.

A useful warning: ότι is different from ό,τι.

• ότι = that
• ό,τι = whatever / anything that

Because η επιβίβαση is the subject of the second clause.

The sentence has two parts:

• Η ανακοίνωση λέει = The announcement says
• ότι η επιβίβαση αρχίζει... = that boarding begins...

Since επιβίβαση is a feminine singular noun, it also takes η.

επιβίβαση means boarding.

It is a fairly formal noun and is very common in travel contexts:

• η επιβίβαση = boarding
• κάρτα επιβίβασης = boarding pass

So in this sentence, it refers to passengers starting to get onto the plane, ferry, etc.

This is very normal in Greek.

Greek often uses the present tense for a scheduled or imminent future event, especially when there is a time expression such as σε δέκα λεπτά.

So:

• η επιβίβαση αρχίζει σε δέκα λεπτά = boarding begins in ten minutes

This sounds natural in Greek.

You could also say θα αρχίσει for a more explicit future meaning, but αρχίζει is completely normal here.

It means in ten minutes.

Here, σε is used for a point in time from now:

• σε δέκα λεπτά = in ten minutes
• σε μία ώρα = in one hour
• σε λίγο = soon / in a little while

This is different from duration:

• για δέκα λεπτά = for ten minutes

So σε δέκα λεπτά does not mean the action lasts ten minutes; it means it starts ten minutes from now.

Because after a number, Greek normally just uses the noun directly:

• δέκα λεπτά = ten minutes
• δύο ώρες = two hours
• τρία άτομα = three people

You do not need an article there.

In this sentence:

• η ανακοίνωση is in the nominative, because it is the subject of λέει
• η επιβίβαση is also in the nominative, because it is the subject of αρχίζει
• δέκα λεπτά is in the accusative, because it comes after σε

For a learner, the most important thing is to notice that σε is often followed by the accusative.

Sometimes Greek can sound less explicit in speech, but in this kind of sentence ότι is very natural and standard.

You may also hear πως instead of ότι:

• Η ανακοίνωση λέει ότι...
• Η ανακοίνωση λέει πως...

Both can mean The announcement says that...

A rough pronunciation is:

ee anakí-nosee léi óti ee epiveevasee ar-khízee se déka leptá

A few helpful notes:

• η sounds like ee
• ει in λέει also sounds like ee
• χ in αρχίζει is like the ch in Scottish loch or German Bach
• the stress marks show which syllable is stressed:
  • ανακοίνωση
  • λέει
  • ότι
  • επιβίβαση
  • αρχίζει
  • δέκα
  • λεπτά

The sentence as given has a very neutral, natural word order:

• Η ανακοίνωση λέει ότι η επιβίβαση αρχίζει σε δέκα λεπτά.

Greek word order is somewhat flexible, but this version is straightforward and standard.

The key thing is that Greek often keeps the structure:

• main clause
  • ότι
    • subordinate clause

So this sentence is a very good model to learn from.