strategy with world market data

[wes7763]

I am new to ninjascript and what I am trying to do is create a strategy where I go long if certain world markets are up and go short if certain world markets are down. But I only want to go long/short on stocks that have just crossed over their 9 and 18 period EMA's. I believe I have to add the world market data series to initialize. And then in onbarupdate state that the close > close of the day before for each world index. I have already added the world index data that I want into instrument manager, but I am having trouble developing the strategy to actually use the index's data. How would I setup this strategy for the world market data. Do I need to add multiple entry signals, or sync data series bars to the primary object, or do I need use barsinprogress to achieve what I want to do?