How to install the One Page Checkout Cart?
The One Page Checkout is installed and published by default. So you dont need to do anything. You want to use the default VirueMart cart you disable plugin (VMuikit OnePage) in plugins in Joomla backend. Or if you want to use another One Page Checkout also disable this plugin first.
All the settings for this plugins you find in that place too. There are quite a lot of settings to make the cart work and look just as you want! Try the setting out to create you streamlined cart experience for your clients!