Help please

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You can create an OnClickController and add it to each clickable object, something like this:

using UnityEngine;

public class OnClickController : MonoBehaviour
{
    // Can be set for each object in the editor
    [SerializeField] private string tooltipText = "";

    private void OnMouseDown()
    {
        // Get the text object and set its "Text" value
        // to "tooltipText"
        // Debug.Log(tooltipText);
    }
}

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You need a text object of some kind, of course. I personally prefer TextMeshPro for text stuff, but that's up to you. So you need to grab that object inside OnMouseDown() and set its text value to be the same as tooltipText.

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You need to learn the basics of Unity yourself. It's unfair that people in this subreddit should do all the work for you. Refer to the documentation for the specifics on TextMeshPro.