Do you have a WordPress.com or a self-hosted (WordPress.org) install? And are you logging in as an administrator?
My address is http://mediasixplus.wordpress.com/, when I log in as an administrator I don’t find the plugin Icon on the dashboard. I wanna add sidebars to pages.
Ah, WordPress.com websites are websites hosted at WordPress.com. WordPress.org is for self-hosted WordPress installation. That’s why you can’t find the Plugins tab.
For support for your WP.com website you’ll have to go to WP.com (these forums are for self-hosted – aka WP.org – websites).
Yes, unfortunately unless you get a hosting plan and upload from .org, you can’t use plugins. That’s the advantage of hosting your own blog rather than have wordpress do it, lots more customizations available.