I presume this post is not about an introduction, rather about technical issues you seek help with.
Not all you mention is clear, like what is adduser-skeleton, and is promt the command-prompt?
But, did you see these things in Live mode? Did you re-use an existing /home partition without formatting? Changed the theme form default Midna?
What is your issue with systemsettings > Accounts Details > User Accounts > adding a user by clicking the + sign? To use cli, see
To be able to help, SysInfo is also needed: