This code shows me seconds and miliseconds after game started. What should I do because I want to show only seconds ?

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

public class TimerScript : MonoBehaviour {

public Text timerText;
private float secondsCount;
private int count;

// Use this for initialization
void Start () {

    count = 0;
}

// Update is called once per frame
void Update () {
    count = count + 1;
    secondsCount += Time.deltaTime;
    timerText.text =" Score:" + secondsCount.ToString();
}

You could simply use Time.time like this. The zero in "Score:0" is what removes the milliseconds/decimals.

using UnityEngine;
using UnityEngine.UI;

public class TimerScript : MonoBehaviour
{
    public Text timerText;

    void Update()
    {
        timerText.text = Time.time.ToString ("Score:0");
    }
}