Updating & Retrieving SharePoint List using Client Object Model (C#)

Step: 1 Add the SharePoint Reference 
              Refer this article 

Step: 2 Add the SharePoint namespace

using Microsoft.SharePoint.Client;

Update the Share Point List

public string UpdateTaskList(string Url, string UserName, string Password, string Title, string Describtion, string ListID)

       {

           try

           {

               ClientContext context = new ClientContext(Url);

               context.Credentials = new NetworkCredential(UserName, Password);

               Web site = context.Web;

               Guid id = new Guid(ListID.ToString());

               context.Load(web);

               List objList = web.Lists.GetById(id);

               objList.Title = Title;

               objList.Description = Describtion;

               objList.Update();

               context.ExecuteQuery();

               return "";

           }

           catch (Exception e)

           {

               return e.Message;

           }

       }

 Create List Table

       void CreateListtable()

      {

          try

          {

              dtList = new DataTable();

              dtList.Columns.Add("List", typeof(string));

              dtList.Columns.Add("Description", typeof(string));

              dtList.Columns.Add("ListType", typeof(string));

              dtList.Columns.Add("ItemCount", typeof(string));

              dtList.Columns.Add("LastModified", typeof(string));

              dtList.Columns.Add("ID", typeof(string));

          }

          catch (Exception)

          {

              throw;

          }

      }

  Retrieving SharePoint List

       public DataTable GetTaskList(string Url, string UserName, string Password)

       {

           try

           {

               CreateListtable();

               ClientContext context = new ClientContext(Url);

               context.Credentials = new NetworkCredential(UserName, Password);

               Web site = context.Web; ;

               ListCollection listcollection = web.Lists;

               context.Load(listcollection);

               context.ExecuteQuery();

               foreach (List listName in listcollection)

               {

                   //Only Task list

                   if (listName.BaseTemplate == 107)

                   {

                       DataRow dr = dtList.NewRow();

                       dr["List"] = listName.Title;

                       dr["Description"] = listName.Description;

                       dr["ListType"] = listName.BaseTemplate;

                       dr["ItemCount"] = listName.ItemCount;

                       dr["LastModified"] = listName.LastItemModifiedDate;

                       dr["ID"] = listName.Id;

                       dtList.Rows.Add(dr);

                   }

               }

               return dtList;

           }

           catch (Exception)

           {

               return null;

           }