How i can define an iniciator of a process?
You define initiators in Studio:
click the Pool (or human step) and then in the details section click Actors.
Then define your actor.
If you are just clicking Run then this should work but it could be that your configuration doesn't have a default user,
Click Server->Configure, under Authentication ensure you have a valid, and working user. For Studio this is by default walter.bates (bpm)
PS: If this reply answers your question, please mark as resolved.