Import users from external database csv file
You can import the csv file using phpmyadmin if it has the correct information in the correct order, or you can put it in the correct order but it may not be the easiest thing.
I think at minimum you need name, username, email, password to import into jos_users.
I think you will have to make the salted md5 password + salt that it is stored in the Joomla database before importing or the added users won't be able to log in.
Two other tables will need updating with the proper info also in order for the users to work properly.
They would be: