Using W,A,S & D to control character.

Copy and paste from the documentation (You just need to change the Horizontal to move sideways instead of rotating):

 // A very simplistic car driving on the x-z plane.
 var speed : float = 10.0;
 var rotationSpeed : float = 100.0;
 
 function Update () {    
 // Get the horizontal and vertical axis.    
 // By default they are mapped to the arrow keys.    
 // The value is in the range -1 to 1    
 var translation : float = Input.GetAxis ("Vertical") * speed;    
 var rotation : float = Input.GetAxis ("Horizontal") * rotationSpeed;        
 // Make it move 10 meters per second instead of 10 meters per frame...
 translation *= Time.deltaTime;    
 rotation *= Time.deltaTime;        
 // Move translation along the object's z-axis    
 transform.Translate (0, 0, translation);    
 // Rotate around our y-axis    
 transform.Rotate (0, rotation, 0);
 }

Link to documentation.

As default, W and S is the "Vertical" string and the A and D is the "Horizontal" string, but you can change this through the Input settings: Edit->Project settings->Input.

Good luck!