Selector
The sole purpose of a journey selector is to assign application groups to existing journeys based on contextual information present on the user authentication session.
This allows to make a decision in selector based on user properties - e.g. Group membership, country of residence, IP address ranges, User behavior (UBA) or for example random selection.
Example of the selector:

The yellow “play” bottom marks the start of the evaluation. When it is selected it offers options on what kind of user engagements are offered at session start for mobile and desktop devices: QR or username input

Transitions with conditions on them lead to journeys that can be chosen for the execution of the authentication. See Journey on how to define transitions.
Drag a Journey box and with it selected you can choose what journey to be applied if the transition is true, and what is the priority of the journey, in case multiple transitions evaluate to TRUE at runtime

Opposed to Journey definition, in selectors multiple transitions can evaluate to TRUE. The chosen journey to be followed will be the one with the highest priority
More information related to this topic can also be found in this article.
User Engagement
An administrator can also enable or disable option of engagement for end users, such as:
QR Scan - enables the existence of the QR code during authentication
User Input - enables user input box during authentication
Certificate - enables the possibility to use a certificate during authentication
