user.rb

class User < ApplicationRecord
  ...
  after_create :start_newcomer_process

  def start_newcomer_process
    template = RailsWorkflow::ProcessTemplate.find_by_title('New User Process')
    RailsWorkflow::ProcessManager.start_process(
      template.id,
      { user: self, url_path: 'user_path', url_params: self }
    )
  end
  ...
end