The WordPress plug-in directory is not the only place you can find great WordPress plug-ins, so when you run across one you’re interested in trying out, go ahead and download it to your hard drive (I suggest creating a folder just for Plugins and saving it there so you can easily find it later.) It will likely be a .zip file, which is what you’ll need.
Login to your Dashboard and click on ‘Add New‘ in the plugins menu at the left. Click on ‘Upload‘ as indicated. You’ll want to upload the .zip file you saved to your computer, and then WordPress will take care of the rest. So, browse to the plugin zip file you downloaded and then click the Install Now button.
WordPress will tell you that it successfully installed the plug-in and ask you what action you want to take next: Activate Plug-in | Return to Plug-ins Page. You want to Activate Plug-in. WordPress will activate the plug-in for you and return you to the plug-ins page. You should now see the plug-in in your list.
See? Spectacularly simple!