STEP 1 : Login to your Wordpress admin account ( Usually yourdomain.com/wp-admin )
STEP 2 : Navigate to Users ( Left Navigation Bar ) -> Add New. Click on Add New
STEP 3 : Fill up to details accordingly. Username/Email/First Name/Last Name ( Important ). THe Website can be left as blank.
For Roles, you can select Subscriber, Contributer, Author, Editor, or Administrator . You can read abour roles here ( Official Wordpress page about wordpress user roles )
STEP 4 : Click on Add New User
Once done, the user has been added, you can inform the user of his login and password information, as well as mention the URL of the Wordpress Admin page. ( Eg. yourdomain.com/wp-admin )