If your website is WordPress then install and enable JetPack. JetPack is included with WordPress.com but has to be installed for self-hosted WordPress. If your website is not WordPress then you'll need a responsive theme/design for whatever platform you're on. More information on JetPack.
- JetPack Mobile theme : https://jetpack.com/support/mobile-theme/
- JetPack: https://jetpack.com
- DIY: https://www.studiopress.com/beginners-guide-responsive-design/