Here there are some SharePoint Object model classes.
In the top SPFarm class is there.
This reference the entire SharePoint Server Farm.
By using this you can create a new farm or you can connect to a existing a existing farm.
By using this class you can browse through the collections of servers belongs to the Farm.
Represent a Site collection.
Represent a web site.
The SPUserToken class represents a token for a valid SharePoint user.
SPList corresponds to a single list instance, whether that is a list of items or a document library.
This defines a reference to a specific item of a list.
This type represents a document library.
This class is used to enumerate the files contained in a document library.
This class is the parent class for SPGroup and SPUser.
This class we need while developing web controls or Web Parts.
This is a very useful class and it has some direct methods to access useful information about current requests.