To select a block of text spanning several lines in the editor just hold down the “Alt” key ("Option" key on Mac) while selecting the text


You can also edit multiple lines with the same method, just alt+select (or option+select) the column.


Then anything you type will be inserted on all selected lines.


As a third option you can hold CTRL (Command key on Mac) and click in different locations to have multiple insertion points: 


Watch this short video to see block and multi-line editing in action: