In order for your employees to take a course, they need a user account. You can easily create or upload users in the Account section.
The Account section can be found under your user name in the upper right.

Note: You need to have the "Admin" role to be able to access the account settings.
Creating user accounts
Under the Users tab, click New User to add new individual users. Alternatively, click Import from .CSV to add multiple users simultaneously.
Enter the user's name and email address in the fields provided. Ensure that the Send Welcome Email check box is selected - otherwise you must inform your user of their login details.
Assigning Trainers
Select the Trainer checkbox to assign this role to the user. Trainers can:
Manage the Assignments of courses to users (note: trainers cannot purchase courses)
View the training progress of all other employees under Reporting
Upload custom training courses and create exams with Course Builder
Learn with courses assigned to them
Assigning Admins
You can also add additional administrators to your account.
In addition to the Trainer's features, Administrators can:
Add new users to the account
Change passwords for other users
Assign roles to users
Delete users
Purchase courses
To grant a user administrator access, first create a user account for them. Once they have a user account, select their name from your list of users.

Then, simply click "Make Admin".

Additional Resources:
Article: How to assign e-learning courses