Extract the zip file and just drop the contents in the wp-content/plugins/ directory of your WordPress installation and then activate the Plugin from Plugins page.
There are two work modes:
Simple mode (this is default): calculation results are shown on
Avtodispetcher.Ru after form submit. Field's autocomplete does not work.
Advanced mode: calculation results are displayed on your site. Field's autocomplete does work. Stylized link "powered by" is displayed in widget sidebar.
You can switch this modes on Settings > Distance Calculator Settings page.