Check out example codes for "unity find gameobject with layer". It will help you in understanding the concepts better.

Code Example 1

void Start()
{
    GameObject objByName = FindInActiveObjectByName("Cube");
    GameObject objByTag = FindInActiveObjectByTag("CubeTag");
    GameObject objByLayer = FindInActiveObjectByLayer(LayerMask.NameToLayer("CubeLayer"));
}

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