Google AdSense showcases Google ads on your blog, with full customization.
The easiest way to install this plugin is to use the WordPress Admin interface. Go to your admin dashboard, find the "Plugins" menu, and click on "Add New". Find this plugin and click on "Install Now" and follow the WordPress instructions.
If you want to download it and manually install, you can again use the WordPress dashboard interface. First download the plugin zip file to your local computer. Then go to your admin dashboard, find the "Plugins" menu, and click on "Add New". After clicking on the "Add New" menu item as above, click on "Upload" (below the title "Install Plugins" near the top). Browse for your downloaded zip file, upload it and activate the plugin.
If you want to manually upload it using your ftp program, unzip the downloaded zip file and, 1. Upload the Google AdSense plugin (the whole folder) to the '/wp-content/plugins/' directory. 2. Activate the plugin through the 'Plugins' menu in WordPress. 3. Go to the Settings -> Google AdSense and enter your user ID and options.