I currently have a basic plan, one domain and one website which is on WordPress. Can I setup a second wordpress blog that is a totally different topic than the first within the hosting and just have a subdomain link to it?
A subdomain is a domain that is a part of a main domain or root domain. Sometimes when you want to create a new site that is related to the main site or when you want to host unique content of you site separately, like the pictures, videos and documents, you may consider subdomains. Unlike domains, subdomains can be created by yourself easily without any fee and most web hosts should allow you to host the sites and subdomains without extra fee. Want to add new domains to your hosting account? Check out this tutorial to add extra domains to Bluehost for free.
How to create a sub-domain in your hosting account with Bluehost?
Log on your hosting account with Bluehost. Click Domains from the primary menu at the top, select Subdomains, then the Subdomains creation page opens.
To access this domain creation page, you can also navigate to the home screen of your cPanel, screen down to the Domains section, then choose Subdomains.
To create a subdomain in cPanel, you need to select the main domain name, enter prefix to the main domain, then you can see this domain prefix is used as the home folder for the subdomain name automatically, you can however change it as you wish. Finally hit the big green Create button complete. You will then get the message saying your subdomain has been created.
Although subdomains are usually used as URLs for different sections of your website, you can also use subdomains to create separate websites just like top level root domains. For example, you can refer to this guide to setup a WordPress site using a sub-domain. You can even host subdomain with a different web host. For instance, your main domain and site is hosted with web host A, and you have another hosting with a different web host B, you can create subdomains in your hosting account with A and point the DNS of the subdomains to B, then add the subdomains to your hosting account with B. Check out previous linked article for more details about this issue.