Wordpress plugin installation is a very simple, straight-forward procedure.

First, download the plugin. Extract the file/s on your computer - it's either one file or a folder with files. If you have 2 folders (a folder in a folder) you'll have to upload the inner one.

Open your FTP client, if you don't have one get a free one like FileZilla. Login to your FTP account with the settings from your welcome email. Navigate to public_html/wp-content/plugins/. In case you have your blog on a subfolder or subdomain, please include that in the above.

Upload the file to the plugins folder or upload the whole folder in case it's more than 1 file. Login to your wp-admin and click Plugins. Scroll down the list until you find the plugin that you've uploaded and click "Activate". That's it you're all done.

In case you need to manage the plugin settings click Options and find the plugin in the menu under "Options", or click Manage and find it in the menu underneath (depending on some plugin settings the plugins can be in Options or Manage).