1. You need to create a folder called my-plugins at the same level as bb-plugins. The folder needs 755 permissions.
2. Unzip the plugin on your hard drive, then upload the complete folder to the my-plugins folder. it should be just one folder, not nested folders. So, the folder with the plugin inside it, not a folder inside a folder with the plugin inside it.
3. Log in to the admin and activate on the plugins page.
Let me just say this was a perfect response, with enough detail for me to install plugins in two seconds.