To add news users go to your dashboard and click on Users and then ‘Add New Users ’ and this will allow you to add up to 15 new users at the same time.  You just need their email address and then you create their username and password and they will get an email with the information and a link to go login.

You can also set their role and if they are not managing the site like you are, then you should probably keep them as ‘Subscribers’. If you make them an Administrator they will have access to the site admin dashboard of which there is only one and access to it depends on the user role. This of course is totally up to you.