When you create a participant type, the invitation link will be created automatically.
It will be displayed under each participant type, in Configuration - Participant Type.
The organizers can use the link to invite participants to whom they want to attribute the hidden participation types.
For example, if the Speaker participant type should not be a choice in registration, the organizers can set it to 'hidden'. Then, they can send the participants the invitation link displayed under Speaker. These participants will register by clicking on the link, which means that the Speaker participant type will be automatically applied to them and they won't have to choose the participant type during registration.
Alternatively, the organizer can use the Add participant feature to create the registration on participant's behalf and assign the hidden participation type. In this case, the invitation link is not needed.