השיעור מתחיל בעוד חמש דקות.

שיעור usually means lesson, class, or sometimes lecture period.
With the definite article ה־, השיעור means the lesson / the class.

In this sentence, the most natural English meaning is the class or the lesson.

ה־ is the Hebrew definite article, meaning the.

So:

• שיעור = a lesson / a class
• השיעור = the lesson / the class

It is attached directly to the noun, instead of being a separate word like English the.

Because שיעור is a masculine singular noun.

The verb form מתחיל agrees with the subject:

• שיעור = masculine singular
• therefore מתחיל = masculine singular

If the subject were feminine singular, you would use מתחילה.

מתחיל comes from the verb להתחיל, meaning to begin / to start.

So השיעור מתחיל means:

• the lesson starts
• the class is starting
• the lesson begins

Hebrew present-tense forms like מתחיל can often cover both starts and is starting, depending on context.

This is very common in Hebrew.

A present form is often used for a planned, scheduled, or near-future event, especially when a time expression makes the future meaning clear.

Here, בעוד חמש דקות clearly tells you the event has not started yet, so מתחיל is understood as starts / is starting in five minutes.

This is similar to English sentences like:

• The class starts in five minutes
• The train leaves at six

Even though the action is future, English also often uses a non-future form for schedules.

Here, בעוד means in, in the sense of after an additional amount of time.

So:

• בעוד חמש דקות = in five minutes

A helpful way to think of it is:

• בעוד X זמן = in X time / after another X amount of time

So the sentence means that the class will begin five minutes from now.

Not exactly.

In many situations, בעוד is the more natural way to say in [amount of time] from now:

• בעוד חמש דקות = in five minutes

אחרי חמש דקות more literally means after five minutes, and it can sound more like something happens after a five-minute period has passed, often relative to another event or action.

So for a sentence like The class starts in five minutes, בעוד חמש דקות is the most natural choice.

Because דקה is a feminine noun, and the number has to match that pattern.

So:

• דקה = minute
• דקות = minutes
• חמש דקות = five minutes

For a masculine noun, you would use חמישה instead.

For example:

• חמישה ספרים = five books

But:

• חמש דקות = five minutes

Because the sentence says five minutes, not one minute.

So Hebrew uses the plural noun:

• דקה = minute
• דקות = minutes

That gives:

• חמש דקות = five minutes

The given order is the most neutral and natural:

• השיעור מתחיל בעוד חמש דקות

Literally: the class starts in five minutes

Hebrew word order is somewhat flexible, so other orders are possible for emphasis, but this version is the standard, straightforward one.

For example, putting the time expression first can add emphasis:

• בעוד חמש דקות השיעור מתחיל

But the original sentence sounds more natural in ordinary speech.

A natural pronunciation is roughly:

ha-shi-UR mat-KHIL be-OD kha-MESH da-KOT

A few notes:

• השיעור = ha-shi-UR
  Stress is on the last syllable.
• מתחיל = mat-KHIL
  The kh sound is like the ch in German Bach or Scottish loch.
• בעוד = be-OD
• חמש = kha-MESH
• דקות = da-KOT

The main stresses are on:

• shiUR
• matKHIL
• beOD
• khaMESH
• daKOT

Yes.

Because מתחיל is a present form, Hebrew often leaves some room that English expresses with either:

• starts
• is starting
• begins

In this context, all of these are close in meaning.
The most natural English translation is usually The class starts in five minutes, but The class is starting in five minutes is also possible.