First attempts in openSCAD

[terrypin]

I'm completely new to 3D Printing and am not a programmer. I've assembled a generous gift of an Ender 3 V2 and yesterday successfully printed a small model from thingiverse, unchanged (3hrs 22m). But now I want to learn how to design my own or, more likely, to customise others' models.
openSCAD-FirstUse.jpg
In thingiverse I found a possibly suitable model called 'Ultimate_Box_Generator ' and Download Files delivered these two files:
Box_Template.scad
Ultimate_Box_Generator.scad

I wasn't sure but chose the second file (62 KB).
Q1: When would I need the template file (12 KB)?




I'd seen openSCAD recommended here and elsewhere so I installed that and opened the file. It looked dauntingly complicated (see screenshot) but the thing that puzzles me most is
Q2: Why are there so many 'errors' in its Error Log and Console?
Q3: What should I have done about them? (What I actually did was ignore them!)

I made my changes: x = 100, y = 50, z = 35. I think I may have also changed the 'wall' to 2.5. (My first attempt at this was directly from thingiverse Customizer. It froze and behaved in other quirky ways, which triggered my search for an off-line version.)

Apparently I could do this trivial editing directly in the code, near the top, or using the marginally friendlier Customizer section. I saved the revised scad file with a new name.

After also reading that Ultimaker Cura was popular I then opened the scad file in that and saved it as a gcode file.
Q4: Must 3D printers be presented with a gcode file, no other types, and in the root of the SD card?
Q5: Is there anything else I should have done in Cura apart from clicking the Slicer button?

The Ender 3 V2 is now printing - despite those numerous 'errors'!

Terry, UK