I need it to subtract the number from the array and then display the array again

You need to subtract the entered number from each element of the array; you can't just subtract it from the array itself.

Your code never actually asks the user for the initial numbers. You just display "Please enter in a number System.Double[]" five times. You need to use Console.ReadLine() to read the numbers from the user.

You should avoid using Convert.ToDouble - if the user enters something that isn't a number, that will throw an exception. Use Double.TryParse[^] instead.

static double ReadANumber(string prompt)
{
    double result;
    string value;
    do
    {
        Console.WriteLine(prompt);
        value = Console.ReadLine();
    }
    while (!double.TryParse(value, out result));
    
    return result;
}

static void Main()
{
    double[] entered = new double[5];
    for (int index = 0; index < entered.Length; index++)
    {
        entered[index] = ReadANumber($"Enter number {(index + 1)}:");
    }
    
    Console.WriteLine($"Before subtracting: [{string.Join(", ", entered)}]");
    
    double number = ReadANumber("Enter the number to subtract:");
    for (int index = 0; index < entered.Length; index++)
    {
        entered[index] -= number;
    }
    
    Console.WriteLine($"After subtracting: [{string.Join(", ", entered)}]");
}