First setup

1. Once the download is finished, extract the ZIP file

don't tell me you don't know how to extract a ZIP file

2. Open the folder where you extracted, then go to matject-main

3. Open matject file
   

If something like this shows up, click Run and optionally turn off "Always ask before opening this file" to avoid annoyance.

4. A screen like this should show up

5. "Read" (Hint: Write yes and enter)

6. Use "common sense"
   Because depending on the situation it may not be the same always. So, a fixed guide won't help here.

TIP

You have to navigate using keyboard buttons.
All actions are labelled with the key to press.

 

You have to "click" for a short time (same as how you press ENTER)
But don't "hold".
Holding may cause it to do something unintended.

You're on your own now