What should I do? I am sad and lack of confidence.

Cheer up!!You can do it!! I know some of american jokes that we are hard to understand. But don't lose your confidence ok? Cheer up!!

Vivien,thank you! I try to my best!!~

just as confident as taking a normal talk, everything will be fine, do it then it will be successful

Don't worry because everyone has different joke's ponit. Telling a joke is a good way to improve our sense of humous.