Sakız çiğniyorum, ama toplantı başlamadan önce atacağım.

Because Turkish usually leaves subject pronouns out when they are already clear from the verb ending.

• çiğniyorum already means I am chewing
• atacağım already means I will throw away

So ben is not necessary. You could say Ben sakız çiğniyorum, ama... but that would add emphasis, like I am chewing gum, but...

Çiğniyorum is the present continuous tense, used for something happening right now.

It comes from the verb çiğnemek = to chew.

Structure:

• çiğne- = verb stem
• -iyor = present continuous marker
• -um = I

Because of a sound change, çiğne- + -iyor becomes çiğniyor-, so:

• çiğniyorum = I am chewing

Turkish does not have articles like a, an, or the.

So sakız can mean:

• gum
• a piece of gum
• the gum

The exact meaning depends on context. In this sentence, it is naturally understood as gum or a piece of gum.

Ama means but and shows contrast.

Here the contrast is:

• right now: Sakız çiğniyorum = I am chewing gum
• later: toplantı başlamadan önce atacağım = I will throw it away before the meeting starts

So ama connects two ideas that do not fully go together: chewing gum now, but not keeping it for the meeting.

Başlamadan önce means before starting or, in this sentence, before it starts.

It is built from:

• başlamak = to start
• başlama- = starting / not starting base
• -dan as part of the fixed form -madan / -meden
• önce = before

The pattern -madan önce is a very common way to say before doing something.

So:

• toplantı başlamadan önce = before the meeting starts

Not always in translation.

By itself, -madan / -meden often has the sense of without doing:

• yemeden çıktı = he left without eating

But with önce, it usually means before doing:

• gelmeden önce = before coming
• başlamadan önce = before starting

So even though the form contains a negative element historically and structurally, in this pattern the natural English meaning is before.

Because toplantı is the subject of the subordinate clause toplantı başlamadan önce.

In Turkish, subjects normally appear with no special ending in the basic form:

• toplantı başladı = the meeting started
• toplantı başlamadan önce = before the meeting started / starts

So the bare form toplantı is normal here.

Because the speaker is talking about a planned action that will happen later.

• çiğniyorum = I am chewing now
• atacağım = I will throw it away later

This makes perfect sense with before the meeting starts, because the throwing-away has not happened yet.

Atacağım comes from atmak = to throw.

Structure:

• at- = stem
• -acak = future
• -ım = I

So:

• atacağım = I will throw away

It is understood from context and left unstated.

The thing being thrown away is obviously the gum, so Turkish does not need to repeat it.

If you wanted to make it explicit, you could say:

• onu atacağım = I will throw it away
• sakızı atacağım = I will throw away the gum

In natural Turkish, leaving the object out is very common when it is already clear.

Yes. Atmak literally means to throw, but it is also commonly used for throw away / discard, especially in everyday speech.

So with something like gum, atacağım naturally means:

• I will throw it away
• I will get rid of it

If you want to be more specific, you could say:

• çöpe atacağım = I will throw it in the trash

Yes, but the meaning is a little less specific.

• toplantıdan önce = before the meeting
• toplantı başlamadan önce = before the meeting starts

The original sentence focuses on the exact moment before the meeting begins, so toplantı başlamadan önce is more precise.

Because Turkish normally puts the main verb near the end, and time expressions usually come before it.

So the order is:

• Sakız = gum
• çiğniyorum = I am chewing
• ama = but
• toplantı başlamadan önce = before the meeting starts
• atacağım = I will throw it away

A fuller version could be:

• Sakızı toplantı başlamadan önce atacağım

But in the original sentence, the object is omitted because it is already understood.