To manage the students of a class, you can go (as class manager or platform administrator) either into the class home page and click into the "Users" tab (third from the left below):

or go into Opigno Administration area and click on "Class administration" ("Content" section). Then click on the "Edit" link for the class you want to modify.

You will get an interface presenting the list of users into this class, with their state (active, pending, or blocked) and their role.

An edit link will allow to modify or remove users.

Register one user to the class

At the top of this list, a button "Add members" allows to add participants to this class.
The interface is as below.
You can type an username in the dedicated field. An "autocomplete" system automatically suggests the matching usernames considering the first letters you have entered.

You can then select the state (active, pending, or blocked). By default you will probably use the "active" state. Note that if some classes have dependencies or pre-tests that needs to be done before accessing the course, Opigno will automatically add the users into these classes with the "pending" status even if you select "active".

You can then select the role of the user before saving.

Bulk register users to the class

It's also possible to add multiple users. To do that, just click on "Add multiple members" instead of clicking on "Add members". You can move the users from the "available" area to the "selected" area, then choose the role for these users and the state, and then save.