Add a Single User or Multiple Users

 Add a Single User or Multiple Users:

To create user, the permission we need is Manage Internal Users

Single User:

• Set Up | Users | New User | Enter the user’s name, email address and a username (should be unique) in email address format
• Select a Role | Select a User License
• Select a profile (As per requirement)
• At bottom, select Generate new password and notify user immediately.
• Check your email (the email address provided above)

Multiple Users:

• Setup | Users | Select Add Multiple Users.
• Select the user license as per requirement. 
• Fill up the details for each user.
• Select Generate passwords and notify user via email | Save

Resource(s): https://help.salesforce.com/s/articleView