If you have your Joomla zipped file, unzip the file in your file server, now if you are working offline localhost, be sure to have a web server xampp or wamp work on its directory, if you have purchased a web hosting account use the file manager then you can extract the files in your public html or any directory you want to save it, if you succeed in extracting the zipped file, configure your website, open a browser type in localhost/joomla or try accessing http://yourwebsite/public_html or just http://yourdomainname/