When you installed your WordPress installation in example.com/wordpress/, you should use the following .htaccess file
RewriteEngine On
RewriteBase /wordpress/
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /wordpress/index.php [L]
In case you installed it in the root of your domain, so that would be example.com/
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
Place the .htaccess file in the root of your domain, using an FTP client like FileZilla and you should be good to go.
I suggest Filezilla as an FTP client.
