Check out example codes for "singleton unity". It will help you in understanding the concepts better.

Code Example 1

public class Example
{
public static Example Instance{get; private set;}

void awake()
{
if(Instance == null)
{
Instance = this;
DontDestroyOnLoad(gameObject);
} else
{
Destroy(gameObject);
}
}

}

Code Example 2

public class Example
{
public static Example Instance{get; private set;}

void Awake()
{
if(Instance == null)
{
Instance = this;
DontDestroyOnLoad(gameObject);
} else
{
Destroy(gameObject);
}
}

}

Code Example 3

#region Singleton

void Awake()
{
	if (instance == null)
	{
		instance = this;
	}
	else
	{
		Destroy(gameObject);
		return;
	}

	DontDestroyOnLoad(gameObject);
}

#endregion

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