Learning to Use a 3D Printer for the First Time

I've been really curious about my brother's 3D printer and how it works. He hasn't been using it much lately, so I asked him if I could use it and learn about it on my own time. He agreed to let me use it for free as long as I pay for the filament, which is the plastic that the machine uses to melt and form into the model/object.

The model of the 3D printer is a Creality Ender 3, and takes size 1.75mm filament. The first things I want to print are stands for my speakers to put on my desk, that way they're pointing a bit higher and I can hear them better. 

Right now I'm setting up Ultimaker, which is a software that will connect my computer to the 3D printer, then I can upload any 3D model to print. I can find the 3D models from a website called Yeggi, with thousands of free community uploaded 3D models specifically for 3D printing.