unity_button_creator.cs

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

public class ButtonCreator : MonoBehaviour {
	public GameObject buttonPrefab;
	public GameObject panelToAttachButtonsTo;
	// Use this for initialization
	void Start () {
		GameObject button = (GameObject)Instantiate(buttonPrefab);
		button.transform.SetParent(panelToAttachButtonsTo.transform);//Setting button parent
		button.GetComponent<Button>().onClick.AddListener(OnClick);//Setting what button does when clicked
		//Next line assumes button has child with text as first gameobject like button created from GameObject->UI->Button
		button.transform.GetChild(0).GetComponent<Text>().text = "This is button text";//Changing text
	}
	
	// Update is called once per frame
	void Update () {
		
	}
	void OnClick() {
		Debug.Log ("clicked!");
	}
}