how do I install hardware

Welcome to Apple Support Communities.

Is the MacBook's built-in WiFi broken?

Did the plug-in USB device come with OS X drivers? Just plug it directly in to a USB port on your MacBook.

If drivers are necessary, OS X should ask to install them.

Then you need to add the device in , System Preferences, Internet & Wireless, Network Preferences, click a + in the left column, and configure a new network connection. If the built-in WiFi is still functional, you need to turn it off. You might need to remove it, at least for the profile using the new USB device.