Re: How do I view the plugins??
In mu-plugins, these are plugins that help your WPMU site administration/installation. You won’t find them in the Plugins list. Most likely they’ll have areas in Site Admin.
The wp-content/plugins are for use by the blogs on your network. Here’s where you’d put wp-stats, akismet, and most of the plugins from https://wordpress.org/extend/plugins.
Here’s how I think of it: if it helps me run WPMU, it goes in mu-plugins. If it helps me or a member blog, it goes in wp-content/plugins.
Everything in wp-content/plugins shows up in Plugins for activation/deactivation.