Administer football championships.
Go to WordPress admin panel, and use the "Add new" option under Plugins Menu. Click on the "upload" item, choose the "wp-football" zip file you downloaded and click on the "install now" button.
All you need to do after that is navigate to your blog's administration panel, go in the plugins section and enable wp-football.
For more information, see the "Installing Plugins" article on the WordPress Codex.