AutoCAD groups most objects in collections. Although these collections contain different types of data, they can be processed using similar techniques.
Each collection has a method for adding an object to the collection. Most collections use the Add method for this purpose. However, entity objects are usually added using a method titled Add<Entityname>. For example, to add a line you would use the AddLine method.
Collections also have some other methods and properties in common. The Count property can be used to obtain a zero-based count of the objects in a collection. The Item method can be used to obtain any object within a collection.