Group - User type explanation

Hi Guys,

Can I get a quick crash course on the various difference between:

a member, an owner and an admin member

in a group. i suppose member is way more restrictive but can I:
-set a user to be owner but not an admin ? or
-an owner MUST be an admin?
-can there be more than one owner ? If so, what this will cause ?
-can there be more than one admin ?
-etc

Thanks guys