Zoom provides a chat function - click the icon at the bottom of the screen that says 'chat'. You should keep the chat window open at all times as it is the only way to submit questions, and the only way you can receive communications from the organisers or other participants who need to tell you something. All questions for presenters should be submitted in chat - the chair will either ask the question for you or else will invite you to unmute and ask your question in person at the end of the talk. If you see a question from another participant which you would also like to ask you can 'like' it to give it increased priority.