First of all it's necessary to get the plugin module archive file. You can develop your own plugin module or download one from this page (.tar.gz files listed on the right).
In order to install a module, you have to unzip or untar the plugin module archive file in the
/modules directory and that's it: the module is installed!
Once installed, a module can be easily plugged in and out through BEdita administration page.
Open BEdita administration page, plugin modules section (module Admin, section Plugin modules). The module you installed in your filesystem should appear among Unplugged Modules, in Admin->Plugin modules page, with a PLUG-IN button associated to it. Press PLUG-IN, and it's done ;)
When a module is plugged-in, it appears among Plugged modules, in Admin->Plugin modules page, and it appears also in every BEdita page, among available modules in the main modules menu.
If you want to plug-out a module, go to BEdita Admin->Plugin modules page, find the module among Plugged modules, click on the associated PLUG-OUT button. Modules can be plugged-in/plugged-out any time, through BEdita Admin->Plugin modules page.