Microsoft SharePoint offers a highly structured server-side object model that makes it easy to access objects that represent the various aspects of a SharePoint Web site.
SPSite: Represents a set of logically related SPWeb objects. Each SPSite object or site collection is represented within a SPSiteCollection object that consists of the collection of all site collections on the virtual server.
SPWebCollection: Represents a collection of SPWeb objects.
SPWeb: Represents a SharePoint Web site.
SPFolder: Represents a folder on a SharePoint Web site.
SPListCollection: Object that represents all the lists in the site
SPList: Object that has members that are used to manage the list or access items in the list
SPFieldCollection: Object that represents all the fields, or columns, in the list
SPField : Object represents a field (Columns) in the list.
SPListItemCollection: Object that represents all the items, or rows, in the list
SPListItem: Object represents a single row in the list