You should add Conditional gateways in automatic role lanes. You can add Conditional gateways in user-defined roles but this does not add any information to the process. The engine runs Conditional gateways without the user's intervention.
You must connect a Conditional gateway to the process flow using an inbound and an outbound transition. An error appears in the Problems View if the inbound or outbound transitions are missing.
Generally Conditional gateways have multiple outbound conditional transitions. You can decide the order to evaluate these transitions.