Hi Kevin,
Welcome to VATUSA. Congratulations on joining the Los Angeles ARTCC. When you connect to the network, are you also connecting to Audio for VATSIM and inputting the correct frequency for the controller? You need to have the frequency in both VRC and AFV, VRC provides the text output and AFV will provide you with audio. Your instructor should be able to help you with specifics tomorrow during your session. Let me know if you need clarification on anything I said here.