That sounds like the function of an addon domain. If you mean to use your own bought domain, then just click on addon domains and then place it there.
Otherwise, if you mean to point your free x10hosting main domain, then do the following:
1. Make your new directory inside public_html, and upload your website (or fill out the directory you want to create when doing a website script installation in Softaculous)
2. Go to Redirects in cPanel to redirect your main domain to your site. Otherwise, go to your .htaccess file and redirect the domain in there.