where is the wordpress plugin directory?

I am a very green non techo newbie. I want to acquire some plug ins. The instructions say
“Once you have uploaded a plugin to your WordPress plugin directory, activate it from the Plugins Management page, and sit back and watch your plugin work.”
Where is the WordPress plugin directory? How do i get the new plugin to go there when i find the directory?
I know this sounds really elementery – but I need this answer. Thanks to the kind soul that will tell me.