Upload the the timesurlat-sociable-plugin folder (not just the files in it!) in your /wp-contents/plugins/ directory. If you're using FTP, use 'binary' mode.
Activate the plugin through the 'Plugins' menu in WordPress.
By default only a few sites are activated when you install the plugin but you can activate many more social bookmarking sites by visiting the 'TimesURL Sociable' settings page in your 'Options' menu in WordPress.