This outline should briefly give you enough information to navigate the Unity global menu if you have no sound.
The Unity panel has a sound indicator integrated in to the menu bar.
If you have just installed and have been unfortunate enough to have no sound, chances are the sound card has been muted.
If you press Alt F10 to enter the global menu bar, arrow Four times to the left that should place you in the sound indicator menu.
The first item you are on by default shows the status of your volume, arrow down once to the mute/unmute item and arrow down another time to the volume adjustment. In this field of the menu you can left or right arrow directly from the menu to adjust the volume.
Subsequent boots should retain your volume.