If you chose to use the Java App you are free to enter a different room if you like. Avoid typing in capital letters. Most people will think that you are shouting at them. Using normal type is just fine when chatting with other people. Choose a nick before you start chatting.
Most people usually choose to ignore someone without a nick.
It can't be stressed enough how much this annoys people. Do not IMPersonate anyone because it either runs them off or makes them angry. Some chat sites, IMPersonation is impossible because those chat sites either show your IP address or your email address automatically. Don't be rude to people when chatting. If someone tells you to leave them alone, leave them alone.