1. Start your computer
2. Login with a valid account for your computer
3. Make a connection to the internet (if you are not running vBulletin locally)
4. Open your Browser (if you are using Windows and the Internet Explorer, there should be a small e-icon next to the Start-Button in the lower left corner of your screen - click it)
5. Point your browser to your AdminCP-Driectory
In a standard installation, this is
http://www.yoursite.com/forum/admincp
6. Login with your Admin account
7. In the left frame click the arrow next Plugin System to expand this group
8. Click Download/Upload Plugins
9. In the from, click browse to select the XML on your harddisk you previously saved there (in step 0)
Or in other words: Just import the plugin XML