Also called the Composer Web Installer, and introduced in Tiki18, this feature is for the installation and management of external software packages using Composer
Composer is used in the Tiki code development process to import and manage external software such as jQuery and Bootstrap. But some software cannot be packaged with Tiki due to an incompatible license, or shouldn’t necessarily be packaged with Tiki by default because of the software’s specialized nature or niche application. So it is a natural step for Tiki site administrators to be able to use Composer to install and manage external software specifically for their site after the site is installed.
You can read all the details directly from the Tiki documentation website at https://doc.tiki.org/Packages
Download from the list of packages below the one corresponding to your version of Tiki, currently there are packages provided for Tiki TRUNK , Tiki 21.X , Tiki 20.X , Tiki 19.X and Tiki 18.X .
After downloading the zip file, extract the zip file and copy the resulting folder to your Tiki installation, inside the folder "vendor_custom" that is located in the root folder of your Tiki installation, like the example below for the package "PdfJs"
And it's done! Tiki will pick up the package automatically and you will be able to use it as soon as you enable the preference that requires that specific package.