To mix explicitly, select all the tracks you want to mix together then choose either Tracks > Mix > Mix and Render or Tracks > Mix > Mix and Render to New Track (shortcut Ctrl + Shift + M).
To mix explicitly, select all the tracks you want to mix together then choose either Tracks > Mix > Mix and Render or Tracks > Mix > Mix and Render to New Track (shortcut Ctrl + Shift + M).