tawk.to is a free live chat app that lets you monitor and chat with visitors on your website or from a free customizable page. No catch. No spam. No wares. It's truly free and always will be.
Copy files to your Zen Cart directory. Zen Cart uses customized directories for admin so you have to copy files from YOUR_ADMIN_FOLDER to folder where you have moved Zen Cart admin files. Same thing applies to templates, copy includes/templates/YOUR_TEMPLATE content to folder with template you are using
Go to administration page -> tools -> Tawk.to widget and select widget you want to use in your Zen Cart store, selected widget will appear in all the pages of your store.