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.

Cube script:

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);