You may want to add a second website to your account to utilise its capacity or put up a second website which can be used for testing purposes such as a new design. Either way, it is very easy to do. The question is whether you own a new/alternative domain or whether you are looking to make use of your current domain by adding a subdomain to it - for example with a subdomain, if you owned www.your-domain.com, you could create blog.your-domain.com without any added cost and have a completely different website for it.
For this you would need to create a 'Subdomain' on your cPanel account.