How to install
There are two main ways how to do it. First way is automatic installation through your WordPress and second is manual download from plugin site.
Go to your WordPress admin panel. Click on Plugins in your left menu and then on Add new. Type "liveagent" into the only textbox on page and hit Search Plugins.
You should see plugin listed in the list. Now all you should do is hit "Install now" link and then confirm the question
After you hit OK installation process start and and install the plugin (for more info about WordPress installation process go here).
After this step plugin should appear in your plugins list. Go to Plugins (in your left menu).
First go to plugin home page.
Now download plugin ZIP archive by clicking on Big orange button Download version x.y.z
(x.y.z is always actual stable version of the plugin)
Now you must unzip this directory to your WordPress installation directory into wp_content/plugins subdirectory. Or you can use upload tab inside WordPress to do this.
After successful installation, plugin should be available in your WordPress plugins list.