problem: cyberduck to install plugins

For some reason, I try to log onto cyberduck to add a plugin and it does not work. I have tried typing in studyabroadchat.wordpress.com and then I know both my username and password to edit the wordpress account.

Is there something that I am missing that I should be doing to be able to log onto cyberduck so that I can install plugins?

I find this process of installing the ability for my wordpress page to have plugins very difficult. What is the easiest way to get plugins and if this is the only way then can someone please tell me what I am doing wrong?

All help VERY appreciated 🙂