using CMS.CMSHelper;

using CMS.SettingsProvider;

using CMS.SiteProvider;

using CMS.DataEngine;

...

        string customTableClassName = "customtable.SampleTable";

        // Get data class using custom table name

        DataClassInfo customTableClassInfo = DataClassInfoProvider.GetDataClass(customTableClassName);

        if (customTableClassInfo == null)

        {

            throw new Exception("Given custom table does not exist.");

        }

      // Initialize custom table item provider with current user info and general connection

      CustomTableItemProvider ctiProvider = new CustomTableItemProvider(CMSContext.CurrentUser, ConnectionHelper.GetConnection());

        // Create new custom table item for given class of custom table

        CustomTableItem item = new CustomTableItem(customTableClassInfo.ClassName, ctiProvider);

        // Set value of a custom table item field

        item.SetValue("ItemText", "Sample item text");

        // Insert the item

        item.Insert();