Hi Alaa, plugins do not work like that. Plugins are associated with the entire Moodle, not individual courses. They are accessible for doing things in courses, for example, the plugins relating to Question Types. Each different question type has a specific plugin for it, so you may access a Cloze question, a number of multiple choice questions, in a quiz, but have no need of a short answer question. In another quiz, you might use short answer and essay question types, but no multiple choice or Cloze questions.
All plugins do something specific, we may not use all of them, ever, but they are available to us if we need to. For example, I prefer to use the Page and Book Resource types, for static information, a File resource for downloadable files, not often, mainly using interactive PDFs for an Assignment activity. I can't recall the last time I used an IMS package. It's there if I need it, but it doesn't matter if I don't. I often use the URL
to link to an external web site, unless that site is barred for some reason, in which case I download
the resource and upload
to my Moodle.
Activity types are really wide ranging and while I use a lot of them, I don't use every one of them in one course. No need, as different courses have different activity requirements. Each activity has its own plugin, but I wouldn't delete any of them, never know when one might come in handy.
Hope this helps your understanding of Moodle, Cheers