How to fetch the value of a column from a sharepoint list

May be below snippet taken from MSDN will help you:

using (SPSite siteCol = new SPSite("http://server/sites/Contoso"))
{
    using (SPWeb web = siteCol.RootWeb)
    {
        SPList list = web.GetList("/sites/Contoso/Lists/Books"); SPListItem item = list.GetItemByIdSelectedFields(3, "Title", "ISBN", "Retail_x0020_Price");

        String bookISBN = (String)item["ISBN"];
    }
}