How to resolve Class, struct, or interface method must have a return type?

Not sure what you were trying to achieve, but looking at your code, I have corrected these points to make it execute properly and have commented out the code so that you can understand

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        public static void Main(string[] args)
        {
            //Create insatce of Class with Name as "Lenove"
            Laptop Lenovo = new Laptop("Lenovo");
           
            //Using the above instance called the Price Method of Lenovo class, it will print $1000
            Lenovo.Price();
            //Using the above instance called the Price Method of Lenovo class, it will print i3
            Lenovo.Processor();
        


        }
    }
    //Laptop Class inherited from LaptopBase class
    public class Laptop : LaptopBase
    {
        public Laptop(string LaptopName) : base(LaptopName)
        {
            //this is used to set value of constructor
            this.LaptopBase = LaptopName;
        }

        public string LaptopBase { get; }
    }
    //Laptop Base class
    public class LaptopBase
    {
        public LaptopBase(String LaptopName)
        {
            //use Console.WriteLine to print data
            Console.WriteLine(" " + LaptopName);
        }

        public void Price()
        {
            Console.WriteLine("$" + 1000, "$" + 2000, "$" + 3000);
        }
        public void Processor()
        {
            Console.WriteLine("i" + 3, "i" + 5, "i" + 7);
        }
        public void Ram()
        {
            Console.WriteLine(2 + "GB", 4 + "GB", 8 + "GB");
        }
        public void HDD()
        {
            Console.WriteLine(500 + "GB", 1 + "TB", 1 + "TB");
        }
    }
}

try to execute it here online, it will work and provide you some output