This plugin creates lists of custom field information in the form of sidebar widgets.
Put the files and the folders from the .zip-file into a separate folder in the main plugins folder (e.g. /wp-content/plugins) of your weblog. The files should be stored in a path like this
Files of the plugin:
custom_field_list_k2_widget.php (move this file into the /app/modules/-folder (e.g.: /wp-content/themes/k2/app/modules/) of the K2-theme if you are using the K2 theme with the old sidebar manager or the comparable plugin)
readme.txt (all about this plugin)
Since WP 2.7 you can upload the .zip-file at once and the files will be put in the right place automatically - except for the K2 theme file.