Hi,
Shared hosting is in which multiple sites are hosted on a single server. Every accounts shares space with other accounts,shared hosting is cheap and considered for small websites.
VPS is almost the same as dedicated server, but you don't own the server, it's actually separating a physical server into several independent hosting spaces. You will have full control of your VPS with root access which will allow you to access the virtual hard disk, RAM and to reboot your private server from other VPS as well.
Hope that helps explain the concept
