Simple Grid theme problems

Hi I was hoping someone could help. I’ve just installed the simple grid theme by dessign.net and followed the installation video to the letter but have had the following complications:

1. Can’t get categories I’ve created to show on the front end menu
2. I’ve created a sample post but it won’t display in the grid format with a text overlay as shown in the demo version of the theme
3. When writing a post I’m not offered the option to allow people to comment.
4. When setting a featured image, I don’t get given the formatting options given in the demo video.

Here’s a link to the demo video:
https://www.dessign.net/simple-grid-theme-responsive/

My site is https://www.heistlondon.com

Please please please can someone help?!

Thanks!