Users of Shared hosting all share the resources on the server their websites are on. There is no guarantee of RAM or CPU with Shared hosting. Shared hosting also does not provide full root access to the server, as opposed to VPS package where users are given full root access to perform commands and make configuration changes to their hosting environment.
Virtual private servers have become a popular choice for web hosting because they offer many benefits of dedicated servers at a lower cost. They also provide the added benefit of easy scalability. Since each VPS is virtualized, the configuration can be updated with a software modification rather than a hardware upgrade. Still, dedicated servers often provide better performance since all the resources of the physical machine are dedicated to a single server.
The main reason that someone signs up for a VPS is that they need a server through which to run their site. When you adopt one, you should notice that your site is performing better than it was on a shared account (because of the guaranteed allotment of resources). Also, the full root access gives you better control. You are able to install and get rid of whatever programs you want.
A VPS runs its own copy of an operating system (OS), and customers may have superuser-level access to that operating system instance, so they can install almost any software that runs on that OS. For many purposes they are functionally equivalent to a dedicated physical server, and being software-defined, are able to be much more easily created and configured. They are priced much lower than an equivalent physical server. However, as they share the underlying physical hardware with other VPSes, performance may be lower, depending on the workload of any other executing virtual machines.