All devices on the Web are recognized by a specific number called an IP address, for example 188.8.131.52. When you have a website, the domain that you type to be able to access it is for your convenience, yet the server where your website files are still has an IP address. Since there are a lot more websites and devices than there're IPs, all shared website hosting servers have a number of sites under the very same IP, while when you use a dedicated server you will have a dedicated IP too. Even in the first case though, you will be able to get a dedicated IP for your sites and host them on a shared server. One advantage would be that you may get better search engine rankings as a dedicated IP often means a faster loading website. Last but not least, you need such an IP in case you plan to acquire an SSL certificate for your website and secure the information that visitors submit on it.