There are three ways to select a group of lines:
Click the select bar to the left of the first line you want to select and, while holding the mouse button down, drag the mouse over the lines you want to select.
Select the first line by clicking the select bar. Move to the last line in the group and hold the Shift key down while you click the select bar there.
If you use only the keyboard, place the cursor on the first line you want to select and hold Shift down while you use the up or down arrow to highlight the lines you want to select.
Selecting Several Single Lines
Selecting Separate Groups of Lines
Selecting all the Lines in a Window