It’s always a good idea to have a Master Fader: use the Track> New… menu command, then in the New Tracks dialog screen, enter “1”, then select “stereo”, and “Master Fader”.

A Master Fader’s volume meter shows the combined level of all the active tracks. If the audio on the Master Fader’s meters goes into the red, you must reduce the level on one or more tracks. If the master levels look low, you can raise the volume of your track(s).