public class RetrieveCustomEntities

    {

        public OrganizationServiceProxy serviceProxy { get; set; }

        public void RetrieveustomEntity()

        {

            var clientCredentials = new ClientCredentials();

            // input the user name

            clientCredentials.UserName.UserName = "your user name";

            // input the pass word

            clientCredentials.UserName.Password = "Your Password";

            // input your instance svc url

            using (serviceProxy = new OrganizationServiceProxy(new Uri("url"), null, clientCredentials, null))

            {

                serviceProxy.EnableProxyTypes();

                // input the logical name of the entity

                var query = new QueryExpression("entity logical name");

                query.ColumnSet = new ColumnSet();

                query.ColumnSet.AddColumn("condition");

                var retrievedValue = serviceProxy.RetrieveMultiple(query);

            }

        }

    }