translate ..... .. .

function Update () {

//This will check if your object's position is (0,0,0).

if(transform.position == Vector3(0,0,0)) {

   //Lets move your object.

   transform.Translate(speed * Time.deltaTime,0,0);

}

//This will check if your objects position is (10,0,0).

if(transform.position == Vector3(10,0,0)) {

//Lets move your object back but slower, like you want.

transform.Translate(-speed/2 * Time.deltaTime,0,0);

}

}