Sticky Header

HI, I have just taken over responsibility for this site. It seems there is a sticky header and navigations, but there is no option to remove this in the theme customise area. How do I stop this occurring?
Also, the menu on the mobile page doesn’t work, yet I cant find any reference or settings to a mobile menu? I also see this menu option in the customise screens, which appears to be a slide out menu, but it does nothing, and my normal menu is not seen on this screen.
Lastly when I try and create a static home page in the customiser section, if i select a page i get the following displayed as the page instead of any content.
“All Section are based on page and post. Enable each Section from customiser
eg: for slider section : Home/Front Page Settings -> Slider Section -> Enable Slider.
likewise to other sections ”
I’m not overly familiar with CSS, and normally use plugins to create a site, or the standard CMS tools.
Any help would be greatly appreciated.

The page I need help with: [log in to see the link]