Question about graphing indicator

 

I'm somewhat new to plotting graphs, but have learned how to use the buffer and setting the parameters to draw a line, so please keep your answers on the elementary side. What I'm looking for is an indicator that will let me know when one graph line crosses another, and to create an object on the chart that points to the possible entry point. How would I have an indicator tell me when two graph lines cross over each other, and then, how would I draw an arrow on the chart pointing to the intersection? If an example already exists that you could point me to, that would be very helpful as well. Thanks!

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