Hi Jennifer,

It's been a while for me to discover new resources; I am a propagator of Alan's Cooper About Face as IxD Fundamentals, which contains a good description of IxD techniques, including diagrams.

Based on that, the fundamental technique is Scenarios. It is relatively simple then to draw something on the screen when we have a written narrative or storyboard.

https://medium.com/enterprise-ux/design-scenarios-677d63521902

What helped me a lot was a basic understanding of UML. There are tons of resources, but really just understanding the meaning of logical UML symbols can serve as a good baseline to develop your own unique style for communicating interaction design diagrams.

https://uxdesign.cc/uml-for-designers-ux-deliverables-for-complex-applications-fbc15b456fd