Confused with PDO query and prepared statements for SELECT

[Eiolon]

So I am trying to learn PDO and after some reading, I have found that you cannot use exec with select statements, however, if you are using a prepared statement, you can.

 

However, PDO has a function just selecting the data, using PDO::query. 

 

So my question is, how do I know when is the proper used to use PDO::query or the prepared statement route?  I have been able to duplicate the queries using both methods and obtain the same results. 

 

Is the prepared statement needed for sanitizing the data if I am selecting from user input and PDO:query used if I am only doing a general select where I explicitely state what I am selecting for in the SQL statement?