armedbrothers on "How do I upload a plugin?"

I have a wordpress.com blog. I want to add plug-ins. Numerous instructions tell me to download the plugin, extract, then upload the plugin to the wp-admin/plugin directory.

Upload /[name of plugin/ directory to the /wp-content/plugins/ directory
Activate the plugin through the ‘Plugins’ menu in WordPress

First, I cannot fine the Plugins menu on my Admin page anywhere. What am I doing wrong? I don't understand how to add a plugin.