How to hold a conversation? How to explain terms you've already known?

Hello,

I've started to have online English classes from a native speaker by internet. I'm so excited and I need your advice a lot.

I've got a bit halcyon personality. I don't speak too much even in my native language, average 10 sentences a day !!! Until a few days ago I'd done only listening in English, My listening is not too bad. But I do speak gibberish I guess... In the beginning of the classes the teacher asks basic questions all of the students to make us talk and see how much English do we know. How are you? Where are you from? What is happening in your country these days? etc.. very basic stuff... Even though these are very straightforward, I can not hold the conversation. For instant;

-Hi Servet, Can you hear me?
-Yeah
-How are you?
- fine, and you?
-Good thanks. Where are you from?
-Turkey
-What is happenning in your country these days?
-Erm, erm,,, I'm stammering a bit. than I'm building some very bad sentences.
-Okay. good. let's talk to someone else...!

I hate this! I mean it. I must learn how to hold a conversation. How to make it longer. etc. how to draw my teachers attention. What can you suggest me? Can you give me some useful language?. Some interesting things that might make me look smarter or something. I don't know, when the lesson starts, when the teacher puts me on the spot, my heart beats so hard. I can not concentrate at all. I can't explain something even I've already known. For instant;

-Does anybody know what 'whip' mean?
-Erm, erm....

Outside the class! I can explain it like this. Whip is a something in the shape of rope. It may have approximately 2 meters long. And It's generally used to hit someone or something if you are cruel.

Could someone help me overcome it ? Or just you might share your own experiences. Thanks a lot in advance.