You can wear whatever makes you comfortable! There is no strict dress code requiring formal attire. Most attendees wear casual outfits like t-shirts and jeans, and perhaps a sweater in colder weather. The key is to enjoy the music without worrying about your outfit.
Generally, audiences clap at the end of a complete piece. For instance, a symphony has 4 movements, and it's customary to wait until the end of the entire symphony to clap. This tradition helps maintain the musical flow and atmosphere. However, don't worry if you clap at the wrong time; your enthusiasm is appreciated! It's also traditional to clap for the orchestra, concertmaster, conductor, and any soloists as they enter the stage.
Our orchestral concerts usually last up to 2 hours, including a 15-20 minute intermission. Chamber concerts are shorter, typically around an hour with a brief 10-minute intermission.