How to display menus and sidebar while in mobile

I’m using a free theme called ‘Grid Theme Responsive’ by dessign.net. While it works fine the way I set it up on computer, I’m having some trouble trying to display the navigation menus or sidebar widgets when viewing on mobile device (iPhone, etc.). It can be found at: https://www.dessign.net/grid-theme-responsive/ and notice in the image of iPhone on that page doesn’t show any menus displaying pages and blog. I’d like to tweak it a bit.

I really wish to continue using this theme because it looks fine on a computer but not in mobile version where I cannot find other pages or blog. Any feedback would be appreciated!