Michel van Biezen has many videos about many of the topics that will be discussed during ECE 90. He has many different courses for different subjects, but the ECE 90 topics will be under "Electrical Engineering". This Khan Academy course also has many videos and readings discussing ECE 90 topics.
This short video helps explain the difference between series and parallel circuits. It also helps in explaining what happens to current for both circuits.
This video helps you understand the basics of node voltage analysis and how to use KCL to find voltage (I = V/R).
This video helps you understand the basics of mesh current analysis and how to use KVL to find current (V = IR).
Here's a video that will help you understand source transformations. Along with that are some examples that you can try on your own
Michel van Biezen discusses the thevenin theorm and how to transform a linear circuit into a thevenin equivilant.
Michel van Biezen discusses the norton theorm and how to transform a linear circuit into a norton equivilant.