So... What's the difference between istudyguide, lecture notes and e-textbooks?

Despite having gone for the orientation today, I'm still pretty confused about it.

I'm going to assume istudyguide + lecture notes are the minimum we would need to somewhat understand the module to tackle our TMAs and ECA/Written Exam while textbooks basically goes even more in-depth?

Can anyone here clear the confusion? Thank you! 🤣