Managed and unmanaged hosting applies only to dedicated servers (all shared hosting is managed).
Managed hosting means a customer will be able to set up the basics, such as email, domains, etc. but the host takes care of more advanced functions such as maintenance, security, and software upgrades.
Unmanaged hosting is a situation where the customer takes care of everything involving their server. The web hosting company simply provides the physical server and access. This is usually a cheaper option, but should generally only be selected by advanced users.