To “raise one's hand” means to put one's hand in the air to ask for permission to speak, usually in a classroom or in a large meeting.
In the United States, it is often considered rude (or not polite) to speak without first raising your hand and asking permission, especially if you are at a meeting or in a classroom.Shawn says that if people raise their hands, he'll be able to “call on” people one at a time.
To “call on someone” means to say someone's name and ask him or her to speak.In a classroom, the teacher calls on students to answer questions, and in this business meeting Shawn is going to call on the people who want to share their ideas.
Shawn says that this will help to avoid having people talk over each other.To “talk over” someone means to speak when someone else is speaking, so that two people are speaking at the same time, which makes it difficult to understand.
In the United States, in a business setting, you should always try to let the other person finish speaking before you begin speaking, because talking over another person is considered impolite, or rude.Shawn asks people to make sure that their questions are on topic.
To “make sure” (sure) means to be certain of something, or to be careful to do something in a certain way.You might ask your wife to be sure, or to not forget, to go to the store on her way home from work.