To add users, you must ensure you have the permission to add new members (you must be either an owner or a Moderator).
Add user by email
Go to the channel you'd like to add users to (you must be the owner or moderator of that channel to add users)
Click the "members" icon at the top right of the channel.
Click the blue "+add" button at the bottom of the members tab pop up.
Copy and paste your students' emails from your roster into the text box.
Click "add users".
This automatically adds the users to your channel, and auto-creates their Nectir account if they don't have one yet. Users will receive an email with their account information and notifying them they've been added to a channel
Use slash commands within the message bar to add a user by username, or add everyone from a specific room (aka channel)
Go to the message bar within your desired channel or sub-channel.
Type in /invite-all-from #your-room-name-goes-here
Once you enter this command from your message bar, all of the users within that channel will be added to your channel/sub-channel. This makes it easy to add all of your students from the main channel into your sub-channel within it.
You can repeat this command multiple times whenever you need to make sure everyone has been added.
Remember, sub-channels do not automatically add everyone from the parent channel.
How to see who is in your channel or check if they've been added:
Click the "Members" tab in the top right corner.
Toggle the list from "Online" to "All Users". If you have a large group, you may need to scroll down and select "Show More" to see and search the full list.