You can host a basic web application, such as a blog or simple website in a VPC, and gain the additional layers of privacy and security afforded by Amazon VPC. You can help secure the website by creating security group rules which allow the webserver to respond to inbound HTTP and SSL requests from the Internet while simultaneously prohibiting the webserver from initiating outbound connections to the Internet. You can create a VPC that supports this use case by selecting "VPC with a Single Public Subnet Only" from the Amazon VPC console wizard.
If you are not already familiar with Linux system administration, you will need to devote a great deal of time to familiarizing yourself with all of the applications you're using and the CentOS operating system - you could pay someone else to set up your VPS for you, but that wouldn't help down the road when you need to update software and resolve administrative issues... (if you're not sure, go with a managed service)
In this case, providers do not offer any help in case any problems are encountered with unmanaged VPS accounts. The customers should, therefore, have a thorough knowledge of Linux operating system and understand the ways to control the VPS so as to ensure uptime, reliability, and server stability. There may be problems related to resources, software, performance, or configuration- all of them have to be handled by the clients themselves. The web host will only look into problems related to network or hardware in case of unmanaged hosting.
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.