您有太多不需要的Console.ReadLine()，您也需要提前声明和读取decision。您可以尝试以下操作：

using System;

namespace Coding_basics
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.Title = "To Infinity";
            Console.ForegroundColor = ConsoleColor.Green;

            Console.WriteLine("Welcome");
            Console.WriteLine("You have entered the program, press 1 to proceed or press 2 to leave");
            
            int decision  = Convert.ToInt32(Console.ReadLine());
            
            if (decision == 1 )
            {
                Console.WriteLine("Good luck...");
            }
            if (decision == 2)
            {
                Environment.Exit(0);
            }
            
            Console.ReadKey();
        }
    }   
}