I just want to try the office 365 SharePoint Online and I got the trial account for it.
When I created the private site collection the
Administrator is required. How can I create a user for it? Is it available for trial version?
The trial version should be only for 1 user. So you can only use yourself. Even my MSDN Premium doesn't allow more.
Regarding the people picker, mine too show same unless you type some and search.