You can add additional sections to your main domain as a sub-domain. This will help to cover all the different pages on your website. Suppose, your main domain name is example.com and you have a section called sales so you can set a subdomain with sales.example.com. Your data will be stored in the example.com/sales directory inside your file manager. Your page will have a separate identity with a sub-domain.
Nowadays subdomains use as testing platforms before you publish your content on your main or live website. You can also perform the task of updating new updates on your website with the subdomain. Also, there is no negative impact on website SEO with the subdomain.
Adding subdomain is very easy. Here are the links to add subdomain in popular controlpanel like cPanel and SolidCP.
Parked Domain is a domain name that used to point your main domain. It is a registered domain that doesn't link with its own website or email hosting service. A parked domain will be used to park your website for later use. Generally, when you register your domain, it will link with your hosting service. You can purchase a domain from Accuwebhosting.com and park it on your own website. There could be various reasons for parking domain like reserving your domain or to use multiple addresses for your website.
Addon Domain is a separate Domain in your web hosting account. It will have their own email hosting, website etc. Once you create the addon domain, it will have their separate directory within the root folder. For example, if your primary domain name is example.com, you can add the domain.com as an addon domain.
Webmaster widely uses cPanel where there is an option to add the addon domain. Recently, cPanel introduces a new billing in which each cPanel account will be billable. You can add addon domains in your single cPanel account instead of creating a separate cPanel. This will save the cost for another domain. Here, is the link to add addon domain to your cPanel account.