The most basic tutorial of all tutorials: How to move a cube with the arrow keys.
If you are new to Unity, this is a good place to start.

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Cube script:

/* .-------.                             .--.    .-------.     .--.            .--.     .--.        
   |       |--.--.--------.-----.-----.--|  |    |_     _|--.--|  |_.-----.----|__|---.-|  |-----.
   |   -   |_   _|        |  _  |     |  _  |      |   | |  |  |   _|  _  |   _|  |  _  |  |__ --|
   |_______|__.__|__|__|__|_____|__|__|_____|      |___| |_____|____|_____|__| |__|___._|__|_____|
   © OXMOND / www.oxmond.com */

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Cube : MonoBehaviour {

	void Update () {      
             transform.Translate(Input.GetAxis("Horizontal") * Time.deltaTime * 15f,0f,0f);		
             transform.Translate(0f,0f, Input.GetAxis("Vertical") * Time.deltaTime * 15f);		
	}
}