Wordpress is a great site Content Management System (CMS). I've been using it a little - not for this site - and it works well. The only real problem I've encountered is that sometimes you want to add a plugin, and the menu entry that lets you do that isn't there.
How Do I Fix This?
If the "Add Plugins" menu entry is missing, ensure a theme is selected in my site/network admin/themes. If that doesn't work, select your site's default theme, log out, log in again and refresh the web page.
If THAT doesn't work, just go directly to the "Add Plugins" page on your site. It's at:
Why Does This Happen?
There seem to be a lot of possible causes, from broken themes to incorrect file permissions, to some weird programming errors. It seems to be "One of those things" that has lots of possible causes, lots of possible fixes, and hopefully you'll find the right combination eventually.
As for me, I just gave up when everything looked fine (it was a completely new installation) and the option still didn't appear. I'm not a PHP developer, so I just use the direct link to the "Add Plugins" page. Hopefully someone will fix it properly someday.