<p>I recently got a Creality Ender-3, and tried printing a few things for some tests. I’ve printed a cube and just printed a cylindrical tube today, and I notice each time, it adds this random line on the left and a sort of outline around the actual print. Neither of these were there in my Cura file, but they’re always printed and I’m not sure why?</p>

<p><a href="https://i.stack.imgur.com/SyhGh.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/SyhGh.jpg" alt="enter image description here"></a></p>

The outline around the actual print is called
Skirts
. and the random line on the left is called
intro line
it's not necessary you need both Skirt and intro line. The intro line can disable from custom starting gcode settings
A skirt is an outline that surrounds your part but does not touch the part.
The skirt is extruded on the print bed before starting to print your model. Skirts serve a useful purpose because they help
prime your extruder and establish a smooth flow of filament
.  Observing the skirt also allows you to
detect and adjust any leveling or adhesion issues
before the actual model begins printing.
You can easily edit/disable(not recommended) those settings in Cura (or in any slicing software)
In you Cura navigate to
Build Plate Adhesion
settings
Skirt line count:
The number of skirt lines printed around the model.
Skirt distance:
The distance between the model and the skirt.
Skirt minimum length:
The total length of the skirt. This will
override the skirt line count when the minimum length is not reached
yet.