There are two (2) ways to do line selection:

1. Click and Hold Shift

As the title suggests, you can simply click on any line to select it, then hold Shift, and click on another line to make a proper selection :

2. Using the Start-End marking

You can also use "Start" marker to indicate where you clip gonna start. To use marking,

• First click on you prefered line,
• then click on "Start" button at the top menu (or press Z) to mark the line as start,
• then click on the line where your clip will end,
• and then press "End" button at the top menu (or press X) :

Tip: It is recommended to use keyboard shortcut as they help make your tasks faster:

"Click, press Z, click, press X, press C."