Once the NetworkManager service is started (which should have been done automatically for you!), and the applet is running (which is also automatic when you log in), using NetworkManager is a piece of cake. For information on how to get the service started, see the administrators page. NetworkManager will scan for available network hardware and wireless networks. To view the list of available network connections, simply click on the applet.
NetworkManager will automatically connect to networks you have connected to before, but you will need to manually connect at least the first time. Simply select the network or device from the list, and NetworkManager will attempt to connect, asking you if more information is required. If the connection fails, your keys or passphrases might be wrong, so NetworkManager will ask you for them again. Make sure they are correct, and just hit "Connect..." again.
To switch network connections, simply choose another one from the applet's menu.
Drivers that are included in the upstream Linux kernel work best with NetworkManager, because they have been reviewed and vetted by many kernel developers. If the driver isn't upstream, work with the provider of the driver to clean it up and submit it for inclusion into the kernel. If the driver is not completely open-source (like ndiswrapper, madwifi, and Broadcom's wl.o), then driver bugs cannot be fixed quickly and easily, and NetworkManager cannot be guaranteed to work with it. Make sure the drivers you use are top-quality.
NetworkManager uses ModemManager for great mobile broadband device support. A partial listing of supported mobile broadband hardware is on the wiki. If your hardware is not on the list it's likely to be supported, but many devices first appear in a "fake driver CD" mode and must be changed to modem mode using a tool like usb_modeswitch.
In NetworkManager land, there are two types of network configuration: "system" and "user". User connections are exclusively yours; they are not accessible to other users on the system, and often are the right choice for VPN or mobile broadband connections. System connections are available before login and to all users of the machine; NetworkManager will do its best to read your distro's existing network configuration and make those connections available to you. In both cases, you can use 'nm-connection-editor' to view and change your network setup.
Should find a bug, please report it to us in GNOME Bugzilla so we know what to fix! To help get your bug fixed faster you can follow some of the debugging tips on the wiki. Your bug reports help us continually improve the quality of the product.
NetworkManager is distributed under the GNU General Public License v.2, and is Copyright © 2004-2012 by the NetworkManager project.