A database is a collection of objects, such as tables, views, and stored procedures. Although a typical SQL Server installation will have many databases, it will always include the following three: master , model , and tempdb . (An installation will usually also include pubs , Northwind , and msdb .) Every database has its own transaction log; integrity constraints among objects keep a database logically consistent.
Databases are stored in operating system files in a one-to-many relationship. Each database has at least one file for the data and one file for the transaction log. You can easily increase and decrease the size of databases and their files. Databases and their files can grow and shrink either manually or automatically.
Now that you understand database basics, it's time to move on to tables, the fundamental data structures with which you work.