The free edition of NoMachine allows one connection. If you are working on your local desktop (i.e sitting in front of it) and you would like a colleague or friend to connect to it so that they can collaborate on a document or interact with you, they will be able to connect. This is considered 'one connection'. They must install NoMachine (free) or the Enterprise Client for their operating system on their computer or device.

If you are connecting to your desktop remotely, you will not be able to have a friend connect at the same time. This would be considered two connections. If you want two users to connect simultaneously to a remote computer, you should opt for Enterprise Desktop.

Sharing your desktop

When a user which is not the owner of the desktop connects, you can decide if they should be able to interact or just stay in view-mode.

There are two ways a user can connect to your computer to share your desktop. They can connect using the IP address of the computer. In that case, see the chapter Start your first NoMachine connection in the tutorial here: https://www.nomachine.com/support/documents/getting-started-with-nomachine

Alternatively, they can connect to your desktop using the computer's Machine Id, a detail that you must give them. They will require a Network subscription to connect using the Machine Id because this is a feature of the NoMachine Network service. In that case, see the tutorial here to know how to add your computer to Network to get its Machine Id (this is free to do and does not require any subscription): https://www.nomachine.com/support/documents/getting-started-with-nomachine-network

Remember that having a system account on that machine (username and password) is a requirement for anyone who wants to access an unattended desktop.  If you want to let your friend or colleague connect without them having system account credentials, they can connect as a guest. See this tutorial for more details:

https://www.nomachine.com/support/documents/getting-started-with-guest-desktop-sharing