fillin in objects

I’ve tried for the last 3 hours to try to fill in this object. ive followed the glitchy tutorial, while constant glitchy out of range errors, not populating shapes, have to redraw, sometimes doesn’t register at all. Absolute nightmare of software. One of the times the tutorial actually worked but cut off about 10% of my object. All the rest of the times doing the exact same thing has done absolutely nothing at all. Is anyone able actually able to fill in an object, especially one that they designed?

It would help if you let us know what tutorial you are referring to.