Apache is the most common web server available. If you are unsure what web server you are running, it is likely Apache. Therefore, XenForo includes the necessary configuration file in the root directory.
If after uploading XenForo, you do not see an ".htaccess" file in your XenForo root directory, rename htaccess.txt to .htaccess (be sure to include the "." prefix). You should now be able to enable friendly URLs. If, after enabling friendly URLs your XenForo installation does not function correctly, please contact your host to confirm that they have mod_rewrite installed and allow overrides via an .htaccess file.