Rules on how you can use the database, ie. You get the access rights from the database administrator. The act of giving access rights is called grant and the act of taking back these rights is called evoke . It is good practice to start with read-only rights if you are not experienced SQL user. There are many ways to pinpoint the data you need.
Lets start with some useful, but simple examples.
You learn easier if you do these examples with your computer and database. In reality database, table and column names may differ, but most database systems contain demonstration databases. Open the database which has employee records. We have a table Employees which contains names, addresses and other data for each employee of a company. This may fullfill your curiousity, but it is ineffective.