In your program for the evening, you might see a symphony by one composer contains several movements - each listed underneath the title. It is customary to wait until the entire symphony is completed before you applaud. However, if a soloist does an exceptional job, people will clap. Again, follow the leader. What to Wear - Opera is the one art form where people dress up.
Opening night is more formal, but customarily semi-formal attire is fine.
Some wear tuxes and evening gowns, but a suit or a dress is enough. Again, show your appreciation if it's done well. Customarily, applauding at the end of each scene is appreciated. Arrival Time - See Theatre. However with opera, the accumulation of all art forms, patrons can be passionate about performances.