You can use the built-in responsive app to make your website responsive. Please check out the user manual section on this for a good idea of how simple it is: https://www.ultimatewb.com/responsive-app .
In summary, from your Styles admin panel you can turn the responsive app on/off, and customize the setings there, such as uploading a custom menu button rather than using the default, ot setting what pixel width to automatically have you website expand sections/columns to 100% width. The configurations include default suggested values which you may alter based on your website/what you like.
If you use custom formatting/sectioning of your page, this user manual section also includes info on how to make these sections automatically expand to 100% width for mobile devices/smaller width devices - it's as easy as including the class "expanddiv" to your custom coded div.