This AMP was not developed by Alfresco engineers but contributed by community members; it is therefore neither official nor does it come with any kind of guarantee. You are free to use it, however, for whatever you want.
This AMP does not use the TinyMCE instance included in Alfresco but comes with its own version (currently, 2.1.2).
The AMP is installed like any other Alfresco Module Package. Download it from Alfresco Forge. After installing, start the server and take a look at the server log (in case of Tomcat this is catalina.out) to verify that the module was indeed loaded; you should see something like this:
13:04:35,260 User:System INFO [repo.module.ModuleServiceImpl] Starting module 'org.alfrsco.module.WebClientTinyMCESupport' version 1.0.
In order to render a text property as a TinyMCE textarea, you have to configure the Web Client appropriately, by setting a component generator for your property in question. Here is an example: Suppose your model has a property (in an aspect or type) called my:summary which you want to edit using TinyMCE. Edit your Web Client configuration file to contain (within the aspect/type section):