Error: AddItemName Is a field but it used as type C#

I am developing chat application but there are some errors so plz tell me solution ....

Error :IsRequired does not Exist and ; required

Error line: [ConfigurationProperty("ForumSettings", IsRequired = true)]

Error:ConfigurationCollection doesnot exist

Error line: [ConfigurationCollection(typeof(SettingsCollection),

Error: AddItemName doesnot exist

Error line: AddItemName = "add",

Error: ;Expected (if ; give then also shows error message)

Error line: RemoveItemName = "remove")] 

Error: AddItemName Is a field but it used as type

Errorror Line: private object ConfigurationCollection(Type type,AddItemName addItemName,string p,string p_2)

 Error:RemoveItemName  Is a field but it used as type

Error line:private object ConfigurationCollection(Type type,AddItemName addItemName,string p,RemoveItemName removeItemName)

using System;
using System.Collections.Generic;
//using System.Linq;
using System.Web;
//using SettingsCollection;


/// This class is handling my custom forum settings (Section12.AppSettings.ForumSection).
public class ForumSection : System.Configuration.ConfigurationSection
{
public  string ClearItemsName;
public string RemoveItemName;
public string AddItemName;
    public ForumSection()
    {
        [ConfigurationProperty("ForumSettings", IsRequired = true)]
        [ConfigurationCollection(typeof(SettingsCollection),
            AddItemName = "add",
            ClearItemsName = "clear", 
            RemoveItemName = "remove")] 
        
    
private object ConfigurationCollection(Type type,AddItemName addItemName,string p,string p_2)
{
    throw new NotImplementedException();
}

private object ConfigurationCollection(Type type,AddItemName addItemName,string p,RemoveItemName removeItemName)
{
    throw new NotImplementedException();
}
SettingsCollection ForumConfig
        {
             get
            {
                 SettingsCollection set = (SettingsCollection)base["ForumSettings"];
                 return set;
            }
        }
}