The installation of the plugin is just like any other plugin installation for WordPress. Login to your WordPress site and go to Plugins > Add New.
At the Install Plugins Page click on "Upload Plugin" from the top button.
Then click on Choose File and go to the location on your computer where you saved the downloaded plugin zip file ("edd-deals.zip") and upload this zipped file. You DON'T need to unzip the file. After the plugin has been uploaded, click on the "Install Now" button.
Wait until WordPress has uploaded the file. If it's done click on Activate Plugin.
Now you should see a message "Plugin activated" at the top of the window.
That's it. You just have successfully installed the Easy Digital Downloads - Deals plugin.