Creating a List Item instance programmatically using the object model

Adding a List Item to a Custom List and Get Item ID , Update the list item by Id and delete Item

Using(SPSite sSite = new SPSite(SPContext.Current.web.url)

{

Using(SPWeb sWeb = sSite.OpenWeb())

{

    sWeb.AllowUnsafeUpdates=true;

    SPList sList = sWeb.Lists["PolicyDetails"];

    //Add new item in the list

    SPListItem sItem = sList.Item.Add();

    sItem["Title"] = "Hello Policy Details";

    sItem["Description"] = "Policy Details Description"

    sItem.Update();

    //Get Item Id

    listItemId = Item.ID;

    //Update The List Item By ID

    SPListItem sItem = sList.GetItemById(listItemId);

    sItem["Description"] = "Update Description";

    sItem.Update();

    //Delete Item

    SPListItem iItem = iList.GetItemByID(listItemId);

    Item.Delete();

    sWeb.AllowUnsafeUpdates=false;

}

}

Reference:

https://www.nothingbutsharepoint.com/sites/devwiki/sp2007dev/pages/creating%20a%20list%20item%20instance%20programmatically%20using%20the%20object%20model.aspx